On the core engineering team every one of us tests on IE6, IE7, Firefox and Safari (although we all mostly prefer Firefox and Safari as you can imagine). With that said, I just checked out our intranet, which is running 1.4 using IE6 and I'm not seeing any problems at all.
Is there any chance you've done some customizations via CSS and you've used CSS expressions? I know that can cause IE6 to freeze up sometimes.
I have done some minimal CSS changes, but nothing radical. The only changes were to replace the site logo and the IE6 fix that you posted in this thread:
I've made some template changes, but I don't see how they could cause this problem.
I'll load up a stock 1.3 build and see if I can replicate the problem.
It sure would be nice to get all our users up on Firefox (or at least IE7). It's impossible to debug IE6 problems, when the symptom is a browser hang.