I think the 9200 is the latest graphics card from ATI - it's certainly one of the latest. What it isn't is the fastest, which is the 9800 Pro.
As for your motherboard, most KT400 motherboards will accept the 3000+, but it depends on the actual motherboard really. I can see know real reason why it shouldn't though.
But to be honest, you really won't notice much difference between a 2600+ and a 3000+, and it certainly doesn't warrant the price that you'd be paying.
The AMD Athlon 2600+ does only run at a 166MHz front side bus, but it's really not that far off a Intel. An Intel 2.6GHz processor is only a little (I mean a tiny amount) quicker than a AMD 2600+.
What matters more than numbers is the way that the processor works, and AMD have certainly got a good processor design.