When I right click on a file, the Windows installer "preparing to install" window pops up momentarily, then disappears and the right click drop down menu doesn't open. Right clicking the same file immediately a second time gives me the drop down menu (Open, Run as..., Pin to Start Menu...Properties) I was trying to get to in the first place. This behavior occurs with all file types. It's more of a nuisance than a functional concern, but I'm wondering if I'm missing some obvious solution for stopping it (my OS is Windows XP Professional, SP2)?

Download and run the "Windows Installer Cleanup Utility package" from microsoft.

Thanks so much for the help -- ran the Windows Installer cleanup utility and problem resolved! Never would have come up with that on my own.