Installing both Office 20 via GPO was nothing but a pain in the *ss. Typically we’ve installed most of our software including Office via GPO’s off of a Win2k3 server. Here I work at a community college where they needed to teach both versions of Office in many of my labs. By the way, another option would be to use Office 2003 menus in Office 2007 or to install this flash application that helps in finding the new position of Office 2007 commands quickly. The earlier adopters among your users can move to Office 2007 then, the ones with a more traditional attitude can just stick with Office 2003. This KB article explains how you can run Office 2003 and Office 2007 on one computer. Thus, we're considering letting Office 2003 installed for a while and just offer Office 2007 as an additional option. The only (big) problem I still see is that some of our users won't recover so fast from the first shock. It was not love at first sight, but it can become a passion in the long run. At the beginning, I was quite shocked about the new user interface, but after a while, I come to really love it. I've been working myself with Office 2007 since its release. We will probably deploy this SP soon, although I'm tempted to switch to Office 2007 instead.

Feature summaries can be found in this eWEEk article and at Bink.nu. This KB article has a complete description of the changes in Office 2003 SP3.

Sp3 for office 2007