I completely disagree with the first reply. Your system is clearly limited by the 9600 pro and any of the cards mentioned would provide a nice boost little boost. I can't help you on your pricing, but I'd say good matches best to worst would be 1) X800GTO/pro, 2) 7600GS/X1650 pro/X1600XT 3) 6600GT/ X1600 pro 5) cheap/used 9800 pro (not far behind the last two)
Don't mind the guy that is telling you that your rig will bottleneck those cards.
I went from a 9600XT to a X800 and it was a big difference on my system with a 2600 barton. So, your 2800 won't do that. I also found a nice boost on a X1600, but it's not that snazzy of a card. Cheap, though.
None of the mentioned cards are going to allow the likes of BF2 to be played truly at high res, especially with their lack of pipelines, 800mhz DDR2 memory etc other than maybe the 7600gt but still only 12 pipes.
Alpha wants to run with eye candy, choices are limited these days in AGP. But you certainly arent going to be able to AA or ASF with those cards.
Best bet in AGP is still the 7600 GT, regardless of pipelines... but high res and AA isn't going to happen.
Might squeeze out 1280x1024 resolution iun any given game, but a handful of titles will require lowering a few settings.
PCIe upgrade time for this fellow, and an X1900 XT 256mb at least if high res and eye candy are the goal.