It all really depends on your price limit is. With the R9800pro, you would get faster speeds and slightly better image quality. If money isn't an issue, I would say go for the 9800pro. as for your CPU, a Barton 2500+ would go nicely in your system. I've played around with on of those before and got it up to 2.3GHz with the Thermaltake volcano 11. For the RAM upgrade, if you have less than 512mb, i would suggest upgrading to 512mb. Also, if you run your memory at a syncronous clock with the fsb, you will get better memory performance.
well i know the cpu is fine.
depending on the fsb your getting now and the amount of ram you have now.
if your doing 200fsb and have 512mb get the 9800pro 256mb card
if lower than that upgrade the box first and get a 9700pro