It must be, because I've read another thread where someone who had vista couldn't access saves, and I believe it has to do with user ID permission or something like that. Not exactly sure though...
Myth5, it looks like you got this problem resolved, but I did a search through Tech Support. You may have already found these threads, but, if not, perhaps they'll be useful for future reference:
http://forums.civfanatics.com/showthread.php?p=7026753&highlight=saves+vista#post7026753
http://forums.civfanatics.com/showthread.php?p=5607145&highlight=saves+vista#post5607145