Sometimes very slow when creating thread

I have a program with 6 threads.
At a normal start of the program all is up and running in 4 seconds, BUT
often it takes 3 minutes!?!
What happens is that each "threads->create(" takes about 30 seconds to
create. Print statements before and after and as the first line in the
thread shows that all the time is spent in the "create method". During
that time perl runs with 100% CPU!
Sometime it takes 4 seconds or sometimes 3 minutes to start!
The platform is Win32 (W2000 and XP).
Perl is 5.8.2 and 5.8.3.
Any idea on what is happening and how I could avoid it?
(Its a very large program with a lot of modules used)

thanks
Anders Boström