Microsoft Office 2010 Free Beta
The Microsoft Office 2010 Professional FREE beta is now publicly available for everyone to download. Whilst trying to install this I got an error message stating that "An Office 2003 installation on your computer is corrupted and setup cannot continue. Remove or repair Office 2003 product and re-run setup." This was on my Windows 7 Pro x64 laptop.
I did indeed have Office 2003 installed but I had removed it via the control panel Add/Remove programs before running the downloaded Office 2010 beta. I then tried the Microsoft Office Removal Wizard utility which deleted a whole bunch of other files and assured me no Office 2003 remnants were left but the error persisted (be careful with this tool as it will delete everything in your c:/temp or any-other-drive/temp folder, Office related or not).
Turns out the cause was Visio 2003 which is also part of the Office lineup but is installed and removed as a separate product. After uninstalling Visio 2003 the Office 2010 installer worked like a charm, even though again Visio 2010 has to be downloaded and installed separately (the beta is available here).