The best solution here is probably to have Windows XP with the IBX that is supported by FairUse4WM or freeme2. Get a demo file with DRM protection and make sure the DRM removal tool works for you first. After that contact the service you got the DRM protected files from and tell them that Windows Vista was too slow on your computer so you were forced to downgrade it to Windows XP. Ask the service kindly to re-issue licences for you. After re-acquiring licences, remove DRM protection from them.

Besides freeme2 and fairuse4wm you can use lossy DRM removal software or just screen video capture software that does the same, but is more universal.