FFXI locking upFollow

FFXI works fine on my system, I can log in and play no problem, but for the last few days, about half an hour into playing, the screen freezes up and I have to manually restart the computer. I have done everything I can think of short of re-installing FFXI or Windows. When the game locks up, it is for no specific in-game reason, as far as I can tell. It happens in all zones, whether or not I'm in a pt or in battle or talking or whatever. I've lowered the config settings to the lowest and still have this problem, I've even disabled sound. I've defragged, checked the disc for errors, checked the game for errors through playonline, checked for viruses with Norton and Microhome, run ad-aware, re-installed all graphics drivers and I am completed up to date with Direct X 9.0b and all Windows XP updates. My DSL works fine, no lag. I've asked anyone I know with any knowledge of computers about this, and they all say to post in a forum and ask. That's my problem, I tried to be as specific as possible. Here are my system specs:

Windows XP Home version 2002 Service Pack 1
AMD Athlon XP 1900+
1.60 gHz
512 MB Ram
NVIDIA GeForce4 Ti 4400

Please let me know if you need more info, and please help.

Thanks,
Evan McBeezle

yes, given the consistant time, that definitly seems like a heat issue. check yur graphics card fan, also see if you can fit anymore fans into your case, and blow out any dust that is inside.