personaly i would go with the TI, i have seen better results with the TI, dx9 compatibility is not a big thing right now but it wold be usefull to have for the future, but if u want a good DX9 card go with ATI
might not get some effects but it will play faster at higher resolutions..
as for doom3... it is essentially a dx7 level game... so I am not sure your friend will miss out on too many effects... naturally the newer cards will be more efficient and have some new kewl stuff to run the shadows and bump-mapping effects better/faster.. and render some of the other effects while the 4600 can't... BUT... doom3 may still be almost a year away from the looks of it..
also... agp 4x-8x == almost negligible difference in real world performance...
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS