Did you research this and read http://social.technet.microsoft.com/Forums/en/w7itprosecurity/thread/f1244f8b-5b6c-47d3-bfa3-3de9d26514f9
I like that answer about the XP Compatibility checkbox causing it.
When I have MS Office 2007 installed on my Dell running Windows 7. When I open Excel in opens fine. When I open Word a User Account Control box appears and I have to click on Yes to get into Word. Anyway to change this short of turning off my User Account Contro?