Just for future reference in case anyone pulls this up in a search:

Outlook is the only Office application where multiple versions cannot exist side-by-side on the same computer. You can have copies of other Office applications, such as XP, 2003, 2007, and 2010 versions of Word, Excel, Powerpoint, etc, all on the same computer. However if you try to install Outlook 2010 on a computer that has 2003 or 2007, it will uninstall the earlier version of Outlook prior to installing the new version.

If you uninstall Outlook 2010, you'll need to reinstall the old version of Outlook. And, as experienced by David, there may be issues accessing the existing Outlook profile.

-SW