Usually webcams have an IR filter because of the sensor is sensible to IR light and this would traduce in a quit blurry colored image.
So, the webcam doesn't receive IR light.

Are you looking for the IR-effect or you do want to use IR light to detect position or similar?

In the first case I guess you could just extract red channel from RGB and reduce brightness a bit.
In he second case you could use background subtraction.

you can remove those filters.
check out this tutorial for exampl e: http://nuigroup.com/forums/viewthread/4189/

you also could use the kinect, since it has two built-in cameras (IR and Video).