Supposedly, XP SP2 will give you the ability to have one user logged in locally and one user logged in remotely, over Remote Desktop. According to this FAQ from Windows and .NET Magazine:
1. Start a registry editor (e.g., regedit.exe).
2. Navigate to the
Server\Licensing Core registry subkey.
3. From the Edit menu, select New, DWORD Value.
4. Enter the name EnableConcurrentSessions, then press Enter.
5. Double-click the new value, then set it to 1.
I’ll have to give it a try when I finally install a production version of SP2.