What's my best bang for buck upgrade option

Here's what I have:

Athlon 2700xp (2.16ghz)
Radeon 9800pro AGP
1gig ram

The only game I really play right now is WoW. This setup still leaves a little to be desired in terms of graphics performance. So, the only two things I'd really upgrade are the cpu and graphics card, or both, I can't add any more ram : . Would just a graphics card upgrade be worth it or would I be hindered by my CPU? What's the highest CPU upgrade I can go for? Would that be worth it? Ultimately, would a graphics card upgrade do enough to give me better game performance or should I just wait it out and upgrade everything at a later time?

All I do in WoW now is either 40/20 man raid, or group pvp - 10v10 or 15v15. So it's a lot more demanding than solo play or those benchmarks. My comp handles the solo stuff fine and I could have everything at max @ 1024x768, but when raiding with 40 players and lots of lil critters running around the screen stresses the frames per seconds. I now run at 1024x768 with all graphic settings on min except for distance (which won't affect performance in instances when raiding) and it's still a lil too slow for me. Here's my motherboard...

http://www.biostar-usa.com/mbdetails.asp?model=M7NCD

I was looking at the x800XTs, seems like a great deal for a good upgrade. However, with 40players and other shit on screen, would I still be held back by my cpu?