Have you changed anything about the system lately? Upgraded to Tiger, installed new components etc? If not, it can never hurt to test if it works with a fresh user account.
But, do you really need IE? As it is abondoned by Microsoft for the Mac, the further the system progresses the less stable and good I üresume Internet Explorer will work. If you want to test your sites with a browser that works under Windows as well, I would go with Firefox or Opera