Most graphic cards have a "boiling point" of around 125*c (give or take). Thats when permanent damage is possible, or expected. Temperatures beneath this point can still cause problems, artifacting, shut-downs etc.. these temps differ from card to card.
The 8800gt can go up to 80*c or alittle more and it can be considered normal. 90*c might be a bit too high, 100*c, definitely consider aftermarket cooling, or some better thermal paste. ( I don't have a 8800gt, maybe some dudes who do can pipe in)