What I should do in this case:
1. Use the 2007 CD to uninstall Word, Excel, Powerpoint, OneNote 2007.
2. Use the 2010 setup to install the 2010 versions.

I don't know what Outlook 2007 thinks about it. But it might work. If not, your alternatives seem to be:
- go back to Word 2007
- go forward to Outlook 2010
- use Outlook's native editor in stead of using Word
- use a totally different email program

Kees