I have both 2004 and 2008 - no problems whatsoever. However, the 2004 PowerPoint does not launch under 10.6 and one needs to reinstall Office. But you can leave all Entourage identity files (even Office identity) intact. If you want to get Office 2008, be aware that the home and student edition does not have Entourage Exchange server support if you are to use it. Only the more expensive versions do. But they may be much cheaper on E-bay (this is how I got mine).
I'm hearing about severe compatibility problems between Entourage and Snow Leopard. I haven't upgraded to Snow Leopard yet and definitely won't until Entourage, Word, Excel & PowerPoint work with it. Anyone having difficulties?