Whenever I run into a weird bug or workaround I like to do a short post about it. Doing so helps the community and it is also self-serving in case I run into it a year or so later after I've long forgot about it. Today is one of those times.
My latest disk batch came for my MSDN subscription and I decided to upgrade Expression Blend and Web to version 2. Granted I haven't really used these tools too much, but I plan on doing so in the future. The installation of Blend went without a hitch, but Web failed indicating that I was out of disk space. I have about 40 GB free so I know that's not the issue.
A quick Web search on http://search.live.com (I don't like Google) led me to a forum post somewhere that explained that the problem seemed to be with Office. I wasn't going to go through that today, so I decided that perhaps it was something about the Office installation. The only thing that stood out to me was an add-in for saving to a PDF document. (My company is in love with the PDF format for same reason.)
Removing that would be easy enough, so I uninstalled it and tried the Expression Web installation again. Sure enough the installation completed without a problem. I then reinstalled the save to PDF add-in for Office and I was on my way again.