How to avoid overwriting existing Tbird local folders on new system when moving local folders from old system?

I will be migrating my system from an old slow PC (windows XP) to a new faster PC running windows 7. Thunderbird is running on both systems, with local folders on both. Some, but not all, local folders have the same name on both systems. How do I move the content of the old system's local folders to the new system without overwriting what's already stored in the new system's local folders? Would it be easier just to rename the old system's local folders, and then just add the incoming (renamed) old system folders to the new systems list of local folders? This would give me a list of local folders (after the move) such as Caribou (new system), CaribouOld (from the old system), Gopher(new system), GopherOld(fromthe old system, Whiskey (new system), WhiskeyOld (from the old system), etc. Similar question for address books. Thanks in advance for any advice.