Domain Slowness With Vista

I have been having problems with speeds on a domain.
I am getting download speeds from Microsoft at around 26K/sec and on my XP
machine, also on the same domain I am getting in excess of 600K/sec.

Also when browsing the internet with FF responses time out, and when I use
IE they usually work fine.


Is this a problem with IPV4 and IPV6 support?
If so, what setting would I need to change either on my DNS server or on my
Domain Controller?

-Thanks