I did not like using external utilities but it is necessary for a gamepad controlled enviroment. Now I am in love with antimicro and my 360 gamepad in my living room pc.
This guide is for a Witcher profile. On a 360 gamepad:
left stick controls movement (you can also walk if you have Flash mod),
right stick behaves as mouse,
dpad left draws steel sword (pressing again switches styles),
dpad right draws silver sword (pressing again switches styles),
dpad down enters non-combat mode,
LT flips OTS camera,
RT show object tooltips,
A+Lstick rolls and leaps,
B casts sign,
X attacks (mouse left click),
Y pauses combat,
BACK quicksaves,
START shows system options (escape),
LB is a modifier for switching styles (A fast, B group, X strong) and Signs (Y for next sign), RB for looting (control+lclick).

You need a text editor, like notepad, and antimicro, which is available at github[https://github.com/Ryochan7/antimicro/releases]. I prefer the zipped version that has no installer; just unzip and run the program. Save the empty profile. Open notepad, paste the script below and save as "witcher1.amgp". Load this profile on antimicro. Your game now has full controller support!

<?xml version="1.0" encoding="UTF-8"?>
<gamecontroller configversion="16" appversion="2.12">
<!--The SDL name for a joystick is included for informational purposes only.-->
<sdlname>X360 Controller</sdlname>
<!--The GUID for a joystick is included for informational purposes only.-->
<guid>00000000000000000000000000000000</guid>
<names/>
<sets>
<set index="1">
<stick index="1">
<deadZone>10947</deadZone>
<diagonalRange>62</diagonalRange>
<mode>eight-way</mode>
<stickbutton index="2">
<slots>
<slot>
<code>0x57</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>0x44</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="8">
<slots>
<slot>
<code>0x57</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>0x41</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="5">
<slots>
<slot>
<code>0x53</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="4">
<slots>
<slot>
<code>0x53</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>0x44</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="7">
<slots>
<slot>
<code>0x41</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="6">
<slots>
<slot>
<code>0x53</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>0x41</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="1">
<slots>
<slot>
<code>0x11000021</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>81</code>
<mode>distance</mode>
</slot>
<slot>
<code>0x57</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="3">
<slots>
<slot>
<code>0x44</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
</stick>
<stick index="2">
<deadZone>12482</deadZone>
<stickbutton index="5">
<slots>
<slot>
<code>2</code>
<mode>mousemovement</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="7">
<slots>
<slot>
<code>3</code>
<mode>mousemovement</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="1">
<slots>
<slot>
<code>1</code>
<mode>mousemovement</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="3">
<slots>
<slot>
<code>4</code>
<mode>mousemovement</mode>
</slot>
</slots>
</stickbutton>
</stick>
<dpad index="1">
<dpadbutton index="2">
<slots>
<slot>
<code>0x45</code>
<mode>keyboard</mode>
</slot>
</slots>
</dpadbutton>
<dpadbutton index="8">
<slots>
<slot>
<code>0x51</code>
<mode>keyboard</mode>
</slot>
</slots>
</dpadbutton>
<dpadbutton index="4">
<slots>
<slot>
<code>0x1000001</code>
<mode>keyboard</mode>
</slot>
</slots>
</dpadbutton>
</dpad>

<trigger index="1">
<triggerbutton index="2">
<slots>
<slot>
<code>0x46</code>
<mode>keyboard</mode>
</slot>
</slots>
</triggerbutton>
</trigger>
<trigger index="2">
<triggerbutton index="2">
<slots>
<slot>
<code>0x1000023</code>
<mode>keyboard</mode>
</slot>
</slots>
</triggerbutton>
</trigger>
<button index="1">
<setselect>2</setselect>
<setselectcondition>while-held</setselectcondition>
</button>
<button index="2">
<slots>
<slot>
<code>3</code>
<mode>mousebutton</mode>
</slot>
</slots>
</button>
<button index="3">
<slots>
<slot>
<code>1</code>
<mode>mousebutton</mode>
</slot>
</slots>
</button>
<button index="4">
<slots>
<slot>
<code>0x20</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="5">
<slots>
<slot>
<code>0x1000034</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="7">
<slots>
<slot>
<code>0x1000000</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="10">
<setselect>3</setselect>
<setselectcondition>while-held</setselectcondition>
</button>
<button index="11">
<slots>
<slot>
<code>0x1000021</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>1</code>
<mode>mousebutton</mode>
</slot>
</slots>
</button>
</set>
<set index="2">
<stick index="1">
<mode>four-way</mode>
<stickbutton index="3">
<slots>
<slot>
<code>0x44</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>250</code>
<mode>pause</mode>
</slot>
<slot>
<code>0x44</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="1">
<slots>
<slot>
<code>0x57</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>250</code>
<mode>pause</mode>
</slot>
<slot>
<code>0x57</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="7">
<slots>
<slot>
<code>0x41</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>250</code>
<mode>pause</mode>
</slot>
<slot>
<code>0x41</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
<stickbutton index="5">
<slots>
<slot>
<code>0x53</code>
<mode>keyboard</mode>
</slot>
<slot>
<code>250</code>
<mode>pause</mode>
</slot>
<slot>
<code>0x53</code>
<mode>keyboard</mode>
</slot>
</slots>
</stickbutton>
</stick>
<button index="1">
<setselect>1</setselect>
<setselectcondition>while-held</setselectcondition>
</button>
</set>
<set index="3">
<button index="1">
<slots>
<slot>
<code>0x58</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="2">
<slots>
<slot>
<code>0x43</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="3">
<slots>
<slot>
<code>0x5a</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="4">
<slots>
<slot>
<code>0x2d</code>
<mode>keyboard</mode>
</slot>
</slots>
</button>
<button index="10">
<setselect>1</setselect>
<setselectcondition>while-held</setselectcondition>
</button>
</set>
</sets>
</gamecontroller>

You do not want your gamepad to behave like that all the time, so you need to tell antimicro to switch profiles automatically. Go to Options, Settings, Auto Profile. Click "Add" and select an empty profile, like the default. Click "Set as Default for Controller". Now your gamepad will behave normally outside of Witcher.
Click on "Add". In "Profile" specify the one you created before, which in my example is Witcher1.amgp.
"Title" does not matter, "Witcher" is fine. In "Applcation" you must enter the game's exe path, which is something like "C:\Program Files(x86)\Steam\steamapps\common\The Witcher Enhanced Edition Director's Cut/System/witcher.exe".
Now your profile loads automatically when you play.

Steam Big Picture has essentially turned my PC into a very powerfull console while gaming. Until SteamOS overcomes Windows, an external utility is needed to control the operating system with a gamepad. I prefer antimicro because it is open source and continually developed. I have a a generic profile for navigating Windows and one for every game that does not have full controller support.
I chose antimicro but I am always open to suggestions. The guide is not totally noob friendly (no pictures!) because I think it is clear enough but I can provide clarifications if needed.