I hadn't realised until today that if you install multiple NIC's or add additional IP addresses to an existing NIC on a machines running IIS, that IIS will grab all those IP addresses.
This was causing me a problem with a media server that i wanted to run on my SBS 2008 machine.
The answer is to tell IIS to listen only on a specified address by issuing
netsh http add iplisten ipaddress=required_ip_address
from a command prompt and rebooting. You can then tell your media server to only run on one of the other addresses and all should be well.