Office 2003's disappearing-reappearing PIAs.
Just in case someone else is running into this problem:
If you're trying to install Office 2003 Professional and want to make sure you install the PIAs as well, you go to the setup components list and look for .NET Programmability Support and are surprised when you just can't find it - make sure you have the .NET Framework 1.1 already installed on the computer before you install Office. It won't show up on the list, and won't get installed, if the framework isn't already there - and it'd be a shame to go and reinstall Office now, wouldn't it?