IRs and motion tracking

hello all,

we are doing a project for the end of semester, and what I am looking
for is an advice about the approach I should take in this scenario.
The setup will be a IR camera and back-side projection and IR leds
that is reflected on a sheet, so when the user puts his hand on the
other side of the sheet, I am assuming it will intersect the the
reflection of the IR and stand out from the background. So it will
be a black/white screen where the user touches will be going to the
opposite color than the rest. What kind of approach should I take for
this? Is there any externals that make my job easier?

Thanks in advance
ilteris.