Two ways to go about this. You can create Addressbook groups, or you can make a second user account within your Mac just to manage the second addressbook. The advantage of the former, you can selectively search between two separate groups of addresses. The advantage of the second obviously is totally separate operation.
http://support.apple.com/kb/HT2486 - explains the Smart Groups feature of Addressbook
Apple menu -> System preferences -> Users and Groups helps you setup multiple accounts. Fast user switching allows you to use a menubar switch to go between two different users.