I'm running xp as well and I get a similar thing happening. I can play for about 5-7 minutes and then the client just closes. No warning, no error message, nothing. I've tried a few of the other suggested fixes, but this doesn't seem to be related to hardware as far as I can tell. I'm running the most recent update of the client, and prior to the update I didn't experience this problem. I can run the client again and am returned to my position just before the crash. But then I can only play for another 5-7 minutes before the client closes again.
I have to say that this issue doesn't make the game very playable.
I'll provide whatever info I can on this, but I'm at a loss as to where to start looking...
*edit*
Disabling sound in the planeshift setup seems to resolve the issue of constant crashes. Another thread suggested playing with the sound/hardware acceleration in windows control panel - I'll try this next. Possibly an issue specific to the background music? This seems to be the only thing I have turned on when the sound isn't muted.