This is an odd problem, probably with a simple answer.
I have upgraded from Windows 2000 server in workgroup to Win 2k3 SBS premium with ISA 2000 domain.
I can access anywebsite i have ever tried....... apart from microsoft.com.
I have checked and re-checked DNS, and all seems good, i have an all open rule in ISA for outgoing trafic requests.
The server has 2 NIC's, one is plugged into a switch, the other is plugged into an ADSL router.