Diablo II is a "walk in the park" compared to what Everquest wants for resources. If you run Everquest with all Models and everything activated, they require at least 512 meg RAM.
If you have 512 RAM, and nothing else running that sucking up your ram, you might be ok, but I'm willing to bet you are not, because you're banging your virtual memory.
Since you have to reboot to get back to normal (this is very drastic, you should never have to reboot for anything), Then you might have a Malware or Virusproblem and now you can add "or a Hardware problem" to you checklist.
If you're running Windows Vista, Longhorn or what ever it they call it now, the minimum requirements for that OS is now at least 512 meg - you''d have to compensate with more mem.
Also, it's possibe you get the virtual memory error because your hard disk is full, or you have some strange settings on it. Could even be your hard disk needs a scandisk, or has some bad sectors.
But, by all means, don't try any of this out either, just tell me you doubt this is the problem and continue posting