Actually, the 9600XT is the faster performing of the two cards here. Most of the time. (The 9800SE 128-bit is about equal to a 9500np; the 9800SE 256-bit roughly equals a 9600 Pro.)
However, why settle for either when a few more bucks can buy so much faster?
1. You might be able to unlock the extra 4 pipelines and get a 9800 PRO
2. The 9800SE is most likely faster. I have a Hercules AIW 9800SE, I could not unlock the 4 extra pipelines, but it oc's to 432 core 720 mem, I'm sure that it beats every oc'ed 9600XT
But you should make sure it's the 256-bit version and the version clocked at 380/680.
I prefer ATI myself but maybe you should get a Geforce FX5900XT they are about the same price and usually faster.