I'm currently seeing an odd problem with one of my machines running Vista. Quite often when I launch IE7 it simply doesn't appear, I can see it in the process list but no browser. I've tried killing the process off and relaunching but that doesn't help. The only thing that seems to work is to kill the explorer.exe (windows explorer) process off (which kills the desktop) and restart that. If it's some Antivirus plugin I won't be amused!