In Mac OS X 10.4.6, if you installed all Microsoft Office 2004 Updates up to 11.2.3, and experience slowness (lags of up to five to fifteen seconds in Word, Excel, Entourage, etc.), the slowness is from Spotlight. The workaround is: open System Preferences, click Spotlight, click on Privacy, and add the 'Microsoft User Data' folder, located in your user's Documents folder, to the list of excluded items.
In Entourage 2004, you will need to disable Spotlight. Open Preferences: Spotlight and unselect 'Include Entourage items in Spotlight search results.'
[robg adds: I have the latest updates installed, and haven't experienced any such slowdowns. However, I don't use Entourage, and I don't work on massive Word documents. If you are experiencing slowdowns, though, this solution might be worth a shot.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060525082728653