Outlook 2003 should have been deleted automatically. If that didn't
happen, I would be very keen on knowing what choices you made in the
setup program, as I have not been able to reproduce this.
If Outlook 2003 didn't get deleted, you should run Office Diagnostics
(Start, All Programs, Microsoft Office, Microsoft Office Tools) to make
sure that no issues from that are affecting your system. You'll have to
live with the remnants of Outlook 2003 on your system in that case.
The only way to remove Outlook 2003 from your system is to first remove
Office 2007 (incl. Outlook) completely and then remove Outlook 2003 via
the Office 2003 Setup program. Then reinstall Office 2007. Do not try to
remove any Office 2003 component while Office 2007 is still installed.
That is a recipe for disaster.
Outlook is the only Office program of which you can always only have one
version installed. This has been the case since the first version of
Outlook.
Patrick Schmid