well, if anyone ever wants to do this, it's easy, because i figured it out:
the two iMacs should be networked and the old iMac's hard drive shared so that the new iMac has access to it. In Entourage, go to File > Import, and say Import from a program (Outlook Express 5). Go through the step by step things. When it asks where to import from it won't find anything to import, but just navigate to the old iMac's Documents > Microsoft User Data and there should be a folder with all your old accounts on Outlook Express. When it asks what to import, I found that it doesn't work unless you do things one at a time, i.e. Contacts, then Messages, then Rules, etc. Then click Finish and there you have it.
Hope this helps someone some day. i doubt it.