Well, then, switch to the 120gig drive and use evox to format the drive. You will need to backup the C partition of the 80gig drive so the 120gig drive will have a dashboard.
Format:
http://xbox-scene.com/articles/hdd-ftp.php
You can search the net for "slayers evox auto-installer". It is a version of evox that will format and restore new and old hard-drives easily.