msbbossx

Alright, so:
Each game controller or game pad produced has its own "product ID" or 'PID'
The problem is that the controller game is looking for has the wrong PID.

You need to go into the file and change it.
This may seem daunting, but it is really very easy.

Go into your program files, then ubisoft, then into "Tom Clancy's Rainbow Six Vegas 2"
One of the folders inside it is "KellerGame" open it.

Inside that go into the "Config" folder, and then open the file "PCKellerJoysticks" (u can just double click on it and it will open in notepad as a text file)

The top few lines will read:
[Joystick0]
ProductName=XBox Controller HID Minidriver, XID
VendorID=***some number (a)**
ProductID=***some number (b)**
Joy1=XboxTypeS_A
Joy2=XboxTypeS_B
Joy3=XboxTypeS_X
Joy4=XboxTypeS_Y

you have to change (a) to 1118.

Now, you need to find out what your Product ID is. Before that though, two very likely IDs are :673, and 1817, so try each of those first.
(to check them, change the number, save the file, and then run the game and try to turn on the "use 360 controller" option in the game.