Don't bother upgrading your CPU. A 1700+ will work fine for any game on the market. I went from a Duron 900 @ 1066 to a 2100+ and barely noticed a difference in games. I felt it the most in DirectX games like Dungeon Siege. Neverwinter Nights hardly blinked. Unreal 2 was a little faster. I doubt you'd see any appreciable difference unless you went to a 3000+ or higher and a 333Mhz FSB. But that's just my opinion.
As for video cards, the 9500 is still the top performer in most things compared to the other two. Ti4600 beats it on a few things, but is not DX9 compliant. I didn't have any trouble with my 9500 Pro and the KT266A chipset (it doesn't like my nForce chip combined with my power supply though for some odd reason). They are a bit power hungry (have their own power connection via floppy four pin power), but tear up games. I went from a Ti4200 to the 9500 Pro and it was a HUGE difference.
I'm far from being anti-nVidia (I loved my Ti4200), but Radeons are just the way to go right now it seems (I've done a fair bit of research regarding them due to some technical difficulties I had with mine - as seen above).
If you decide to go with a Ti4800, I'm sure you won't regret that either.
BTW, my old gaming system was that 2100+ Palomino, 512 PC2100, and a KT266a. Ran everything just fine.