Ive got an Nvidia 7600GT and It's a brilliant card - I can run SH4 with everything except full glare and the post prodution filters ,(I just dont like the look more than I can't run them),at 1280x1024 with a solid 30fps with my rig
From what I read when I was researching for a new card the 7600GT is one of the best AGP card out , though you will need to buy a new PSU as well as it needs more power than the AGP port can supply.