sharing passwords isn't secure :)
There are ways to accomplish this but they all kinda suck.
1- you know all of their passwords and you make a script that auto adds people to the disk.
- 1 person's password changes.. and this is a pain to manage
2- you use auto-encrypt, silent enrollment policy and supersilent install, this will automagically add users to a 100% encrypted disk whenever they log into windows.
- this will not work at pre-boot for the first user's login, they have to login to windows first to get added to the disk
- still a pain if the user's password changes alot
3- smartkeys might work ( i haven't tried this at all)
- another thing that your users may misplace :)
PGP needs to come up with a better way of encrypting and managing machines that are used by a large number of people. It's way too complicated, and i suggest PGP take a look at how other encryption companies are getting past this (hint: Checkpoint FDE)