Your welcome tovertrut. Love to take credit for the fix but alas this was all down to good ol seaching on the net when I myself needed a solution to running the game on XP.
Olly regarding the other two games you mentioned:
Chaos Gate runs on XP without any fixes needed. Easy turn based game to get into and satisfying choosing squads of Marines and Terminators. Most missions consist of searching for artefact or similar. Becomes a bit repetitive and game screen scrolls too fast however.
Rites of War is a hex, turn based wargame that I love just because the Eldar are a cool race. It does get hard quite quickly but its satisfying watch your surviving troops gain experience and boosting the power of your army.
Overall though, out of all of the games mentioned, Final Liberation is the nearest to capturing the original Epic wargame experience.