Same issues here. For me it all started with Java. Windows Installer would crash each time. Tried several different packages, none worked. Then tried Windows Update, got Explorer crash.
Good news is I kinda fixed the Windows Update problem. I did my usual services.msc optimization and now Windows Update works... very strange. Not a fix really, but it gets you there for the future if MS releases some update that fixes this.
I have installed: CCleaner, Eset Smart Security, Firefox, Device Center, Live Suite, Reaper, CCCP, DVD Shrink, Inkscape, MusikCube. On Windows 7 x64, Q6600, ASUS DH Deluxe, Nvidia 8800GT, 2GB ram.
Hah, just found the solution:
Win+r, regedit
navigate to...