Hrm... still, it shouldn't cause
this big of a problem. What's your computer's specs? What's your processor, how much ram do you have, how much free disk space is there, what operating system are you running, that sort of thing. This sounds like a technical problem of some sort, so the more information you can give, the better.
If it's a desktop, have you tried opening it up and cleaning the dust out lately? You're supposed to use pressurized air, but even just blowing on it might help if overheating due to a dust-filled case is you problem. Um, if you've never opened up your case before, be careful not to touch anything else in there, of course.
Do you keep things on top of it or blocking the fan or anything obvious like that?
Have you tried the premade worlds available on the download page?
...there are various CPU monitor programs you can install to keep an eye on your CPU temperature; you might want to track one down to see if that's your problem before you fiddle with anything else. I can't think of a good one off the top of my head, though... perhaps someone else here will know.
[ September 12, 2006: Message edited by: Aquillion ]