The Entourage MVPs have some great solutions for
database issues. Try those to see if one of those works for you.
8 GB isn't too bad. My own Entourage database is more than twice that.

I have been trying to do a few things to shrink the size of my database, though, including:
* Cleaning out my deleted items about once per month.
* Going through my sent mail occasionally, filing stuff that I want to keep, deleting the stuff that doesn't need to be kept.
* If I'm feeling particularly keen (which is to say: if I'm stuck in an airport on a particularly long delay), I'll check to see which of my Exchange folders is biggest (control-click on your Exchange account, select Folder Properties, click on the Storage tab, and wait for it to populate -- it might take a couple of minutes since you've got so much data), and go through that folder to see if I can delete some stuff or move some of the contents to a local folder.
* Moving things to local folders instead of my Exchange account. (Actually, this one and the previous one are more about keeping under my Exchange mailbox size limit than about Entourage database health, but I think of all of that as the same thing.)
* If I haven't accessed a local folder in awhile, creating a backup .mbox file of it and then deleting the folder in Entourage.
* Compacting my database about once per month.
Regards,
Nadyne.