Internet explorer lockup

OS: Windows NT 4 SP6
Software problem in: Internet explorer 6

Problem: If I try to open more than one session of internet explorer the system crashes. I start task manager, select the open sessions that are not responding, then end task. Originaly it started with IE5, I thought upgrading to 6 would rectify the problem, it didn’t. All critical updates have been done. Has anybody experienced this problem before?
Last resort I will reformat the whole system.

P.S. I will award the Techpoints to the best answer even if it does not solve my problem.
Meaning these points will be awarded.