The 9600 pro will work great. It's a marginally slower then a 5900xt but that doesn't matter for what you're playing. I recommend catalyst 4.2 - maybe even 4.0 + directX 8.1. Try to avoid installing dx9 on win98 - it seems to break compatibility with some older dx5 and dx6 games.
Radeon cards are underrated on this forum but the 8500le, 8500, 9000, 9100, 9500 non pro, 9700, 9600 and 9800 are all great cards to have. On the newer cards front, the X800XT (XL/PRO/GTO work as well) AGP has batter backwards compatibility then the 6800 so older games run w/o issues. It's also a marginally faster then the 6800.
The 6800 is too fast for what you want to play and can be buggy in dx6 and older games. The 7950 does not have win98 drivers (and is that even AGP? I think it only comes in PCI-E flavours sans the 7800 witch has an AGP version but it's pretty rare).
The games you plan to play are dx6/7 and openGL titles. Frankly a P3 + geforce 3 or radeon 8500 should run everything quite nicely. If the P4 has HT disable it in BIOS. It's worthless in 98 anyway since it does not support multi-cpu or multi-threading.