I have a retail copy of C&C that I cracked with the no cd fix that works fine under windows xp (single proccessors). I have had problems with my computer at home, though, not running Red Alert 2. It is a dual AMD system running XP. I have not tried Tiberum sun on that system yet. Red alert 2 works fine at work (single processor, win xp). Of note though, I have been reading some of the progress on the new general game and I see for the beta that they have released a fix for multi-processors. I am wondering if all C&C games have problems with multi-processors??
Hope this helps,
Ws-6