Legit Reviews

I came into a HTPC case, new in box.

Has a IR Module, remote, IR Dongle, IR Blaster pretty much the whole IR end of the HTPC thing. Is there any good HTPC Software out there for XP?

That IR Module should work on any PC with an IR port shouldn't it?

Well there are some that are "good" as long as they work with your hardware (tuner etc) so the best thing is to try them out.
Here are some:

GB-PVR (free) http://www.gbpvr.com
MediaPortal (free) http://www.team-mediaportal.com/
ChrisTV (commercial)
Snapstream Beyond TV (commercial)

You can also use HIP (free) to fully customize your remote controls, but could be a real pain if your receiver-remote are not preconfigured
http://www.byremote.com.au/HIP/Default.htm

Don't have a clue about the ir module