A few days ago, Microsoft released a new Desktop Theme for Windows XP named the "Zune Desktop Theme" – even though it looks a lot like Vista, all in black and orange. It fits in with Office 2007's Black skin, so I gleefully installed it.
Everything was fine for a few days until the first time I had to reboot (rather than Standby/Hibernate) – late last night. From that moment on, my Windows Explorer would crash every time you tried to do anything. Windows loaded? Explorer crashed. Tried to open a folder? Expolrer crashed. Save As from Word? You guessed it.
Took me a while to put two and two together since there were a few days between the two, but the solution is to:
a) Uninstall the Zune Desktop Theme.
b) Choose a different desktop theme (Luna, for instance).
c) Reboot.
This solved the problem for me. Even though I'd gotten used to the gloomy Vista-ish look, I won't be reinstalling it any time soon. Your experience might be different, but beware. If you're feeling curious or suicidal, here's the download link:
Zune XP Desktop Theme