Outlook 2003 / Outlook 2007
Outlook 2003 and Outlook 2007 dont work side by side. As Outlook 2007 updates MAPI; which breaks compatibility with Outlook 2003 (my thinking). OL2003 will not work once you have OL 2007 installed. Though OL 2007 works fine; but its not stable (being Beta) and if you dont want to take a risk; dont install OL 2007 when installing Office 2007 beta.