ISA 2004 Authentication

I applogise if this has been asked\answered before but:

From my vista rc2 workstation, whenever I attempt to browse the web etc. I'm
presented with a proxy server authentication box.

In some respects this is to be expected as our systems require
authentication to use the ISA 2004 server, but no matter what combination of
username\password I use, authentication always fails.

That is until I enter the domain admin account, which allows access but is
not obviously practical.

Has anyone else noticed this behaviour, and how did you get round the
problem


Julian