Windows Firewall Client and Vista

I have an issue whereby I log onto my local PC, and then use the Windows
Firewall Client (ISA Client) to connect to my domain.

This works fine in XP but had a compatibility issue with Vista.

I downloaded the latest client for Vista, which does recognise the
connection, but as soon as I try and log into messenger, the ISA Client has a
problem and does not connect.

Any suggestions would be helpful.

Thanks in advance
Peter