Hi,
If you're changing hard drives I don't think export is your best option. Export will essentially mix down your songs to whatever format; making it impossible to separate and continue working later.

Your best bet is to copy the entire location (folder) containing your work to your external drive. That way the core files are there to work with later. Make sure you get the actual audio samples from the program directory too or you'll have arrangements missing recorded audio.

I store all my audio work in folders and sub folders making it very easy to move if necessary and to back-up... something that should be done regularly!

Justin