A quick tip for those who are on a local network and want an Xsession from another box:
Xnest -query remotelinbox :3
This will actually shoot back a full X session, login screen and all. It's really cool - I use it at work a lot. It works with anything that runs X, too, so Solaris and linux and anything else whose x server does xdmcp should work fine. On the host serving up X, you'll need to enable XDMCP in your gdm/kdm/xdm config file (in /etc/X11).