I had a bad time trying to make Mindstorm RIS 2.0 works on Windows XP (SP2).
During setup of the IR tower (after main program installation), precisely when program first tried to comunicate to device, computer was freezed!

As found in internet this is caused while accessing the IR Tower in an Hyperthreaded (HT) CPU's system.

I've found some "work-around" navigating the internet:
1) Setting RIS2.exe in compatibility mode Windows 98/ME and 256 color mode didn't worked
2) Installing Windows 2000 instead of XP (like jumping in the past) didn't tried
3) Disabling HT in Bios and then repair XP installation (too long)
4) Buy an IR Tower SERIAL (not to consider)

I was pretty discouraged by this results until, at the end, I founded this:
THE SOLUTION: http://elvis.rowan.edu/~kay/lego/RIS_installation_info.html

Following this step-by-step tutorial made all perfectly functioning in about 5 minutes ! Thanks

The first XP-Patch is pretty common and easy to find over the internet (in fact this patch just stop the launch screen from opening after every boot)

What make all working is the LEGOTower.zip who include the new version of the driver for the IR Tower!