Xen users - Jan 2013 - 2MB/sec speeds on dom0 when at least one windows guest is running

Why am I getting speeds so crappy and the nodes behave so slowly when
I start windows 2008 machines in domu on them?

I use xcp 1.6 and all the domu''s have xen tools 6.1 installed and
still the machines work awfully slow and they''re practically
impossible to use.

Please help! This is very urgent and critical.

Thanks,
Ciprian