How do I import existing Outlook contact groups into Mac Address Book?

After months of problems with Microsoft Outlook 2011 for Mac, I am switching to Mac Mail. I seem to have successfully imported my individual contacts into Address Book. However, I have been unsuccessful in figuring out how to import group contacts into Mac Mail.

So far I have created .txt files, (a separate one for each group), listing each e-mail address in that group separated by a comma. Can I input this information into Address Book somehow? If not, how else can I import my groups into Address Book in a more efficient way than manually entering them? Manually dragging and dropping names into each new Address Book group is not an option, since I have about 50 groups with 20-50 people in each of them. It would take me extraordinary amounts of time to do that, not to mention the frustration.

A second question: There are many duplicates listed in my address book. When I select Card>Look for Duplicates, it tells me that No duplicates are found. They most definitely exist, however. How can I erase them without having to manually delete each duplicate?