I'll assume you're running the latest version of Tiger.
All your Address Book information is stored within ~/Library/Application Support/AddressBook.
To transfer your address information from your other Mac, there are two ways:
1) On the Mac with the address information you want to keep, open Address Book. Under the File menu, choose "Back Up Address Book...". Save the file, and transfer it to the Mac with the missing data. Open Address Book there, and under the File menu, choose "Revert to Address Book Backup...", and select the backup file. It will overwrite all your existing entires, and mimic the data from the original mac.
2) Copy the entire ~/Library/Application Support/AddressBook folder from the original Mac. Overwrite the same folder on the Mac with the missing data. All the data will be replaced.
Unfortunately, neither option does anything for your syncing issue. In the future, be sure to backup your Address Book regularly. Or you could look at an online sync service such as Plaxo.