Shame on you for saying "Just format"
If I were to run a program such as EasyRecovery, I would most likely get most info back especially if the drive hadn't even been written to... I could probably get a 100% return on data.
Anywho foofoo is right.
IBM, Maxtor/Quantum, Seagate and Western Digital have Low Level Format tools available. They are normally available under the diagnostic tools these companies offer. Also if you aren't sure which one the Low Level Format tool is (as it sometimes is buried in a diagnostic program) it is the diagnostic test that mentions that after the test no data will exist.
Good luck and I definitely recommend completely wiping the drive before shipping out those drives.
Yvo