In case you missed it, Tiger's Address Book comes with an AppleScript to import Eudora's (and other apps) address book entries. I've used it, it works.
Make sure the Scripts menu is enabled -- go to Applications -> AppleScript and run the AppleScript Utility. Enable the 'Show Script Menu in menu bar' item, then quit the app. You should now have a small AppleScript icon in your menu bar. Click it, then choose Address Book Scripts -> Import Addresses. A window will appear, from which you can choose to import data from Entourage, Outlook Express, Palm Desktop, Eudora, Claris Emailer, and Netscape.
For more help with Address Book and AppleScript, open Address Book's help and search on Scripts.
[robg adds: This script isn't new with Tiger; it existed in 10.3, too...]
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