Dear bigjoe:
the address book (should) is at the folder:
c:\windows\application data\Mozilla
from there search for your profile folder of select user50 if you have not create an profile.
if you have back up your address book before on a removable disk, go to your address book (Ctrl + 5) and click tools -> Import, then the browse to the folder where it is back up in and select it. If you have not back them up before, I am afraid you might not be able to recover them.
Hope this helps:
jason TBk