One easy, fairly universal trick is "IMAP".
Get an IMAP account set up (go make a gmail) and add that account to your entourage. Then drag the emails and contacts etc from the one account to the IMAP account.
Let that sync. After it's done, you can then go add the account to wherever else you need it at, and let it sync, and then drag the stuff over, before deleting the IMAP account on both computers.
I remember a few tricky ones, like Outlook 2003, which used "MBOX" files of a proprietary format and would not export anything. Fortunately, thunderbird could open those weird mailboxes, and then I used the IMAP trick to move data over to my mac. I was doing this for a customer, so I then just exported the mailbox from my mac mail to a "more standard" MBOX file which the user was able to import easily into mac mail.
(addressbooks were always the bigger pain, I can't count how many times I saw clowns exporting contacts in SDF files that used " as a delimiter AND let you have " in your contact name. ugh... and then there was the one that would only let you export one contact at a time, by dragging and dropping it to the desktop, to create a .textclipping file... "fortunately" he had only 230 contacts....)
