1. You've re-installed several times before after a Format C: incident/Windows re-install.
2. You've installed on Desktop, laptop, laptop which replaced the first one, Desktop after a Mobo/HDD change etc
3. You've installed Office 2007 (or 2010) after 2003, but wanted to keep an 03 feature, no longer included in 07(10).
None of those - honest!