My friend asked me to install a new HSF on his 9800pro which had a broken fan. After we installed it I could not get his computer to boot with the card inside. He doesn't want to wait for me to troubleshoot and would like to purchase a new card. I'm thinking about getting him a 6600GT. How much faster is the 6600GT AGP than the 9800pro he currently has? Thanks.
The GF6600GT is not hugely faster, but it's a solid 10-25% faster in most low res situations where they would both be forced now.
The other nice advantage of the GF6600 series is that he will now have access to the greater number of games that are starting to use SM3.0 as the minimum requirement for their games (like the new Splinter Cell, RainbowSix Vegas).
The R9800Pro was a beast and a good card with a long life, but at this point the GF6600GT is a solid performer and a better card with no drawbacks in comparison.
If he has the cash though I'd suggest a cheap GF7600GS or X1600-X1650Pro as a better upgrade for longer term enjoyment since they are more efficient at new games (especially using things like HDR), and usually about the same price or within $5-10 of the the GF6600GT.
The 6600GT is better, but I wouldn't buy one, especially a 128MB version. They both suck at Test Drive Unlimited because the game has so few video settings adjustment that a 256MB card is minimum spec. It will play on a 128MB card, but give fps in the teens at the lowest res and settings.