>The problem I encountered is that while this method was executing,
> Squeak was completely unresponsive. I could not open the Process
> Browser, I could not do anything whatsoever in Squeak.

Of course it was; there should be no surprise there at all. There is a 
single active process and it runs until it stops. You can make it stop 
temporarily by deliberately yielding occasioanlly which will give 
other processes a chance to hog the cpu for themselves - but if that 
other process doesn't play nice and yield occasionally you will still 
feel locked out.

There is not any round-robin or timeslicing scheduling done by 
default. You can implement it fairly simply (google is your friend and 
can find many news postings on the subject over many years) if you 
really need it. The potential danger with using such a modifed 
scheduling setup is that most of the image is not multi-thread safe.