We have experienced various issues with Windows Vista running in a Windows 2003 domain. Today we had trouble with a Vista machine sitting on the 'Please Wait' screen before login. Apparently after applying Service Pack 1 the TCP receive window auto tunes itself and this can cause the machine to sit there.
Credit goes to DarnitOL on Blogspot (looks like a useful resource) for the solution.
To boot up, turn of your computer, unplug the network cable, then log in. Once you have a working desktop plug the cable back in.
Now to fix the Autotuning:
Before you begin, reboot your computer into safe mode with networking enabled.
1. Open an elevated command prompt (Run as Administrator).
2. Click on Continue on the UAC if prompted.
3. In the command prompt, type netsh interface tcp set global autotuninglevel=disabled and press Enter.
4. You will get an OK response. If not, repeat step 3.
5. Close the command prompt and restart computer to apply the changes.