This used to work, but has since stopped, the only change being i had the laptop elsewhere, connected in to someone else's home network. The problem showed itself when i brought it back and tried to share the desktop's iTunes library on the laptop - it didn't show. It was then i discovered that RDC didn't work either. The only other change i've made is to update to iTunes 10 on both machines.
Both machines are set up to allow users to connect remotely, the Windows Firewall is off on both machines, they are both on the Workgroup 'HOME', but no domain has been specified. Both machines can successfully connect to the Internet over my BT Broadband service. (I've also checked RDC in the other direction - still no joy)