Having trouble with Migration Assistant

I'm trying to migrate multiple accounts (created on a MacBook running 10.5) from a Time Machine backup to a MBP running 10.6. I'm using an "admin" account on the MBP to run Migration Assistant.

Here's what's happening:

1. Migration assistant sees all the accounts from the source backup, and they are all checked.

2. When it calculates the size of the accounts to be migrated, it comes up with ~80 GB.

3. Migration takes about an hour and a half using a USB 2.0 connection to the extermal hard drive that holds the backup.

4. When migration is complete, and I've restarted my computer and logged out of the Admin account, I don't see any of the migrated accounts among my choices of logins, and only ~20 GB of additional space has been taken. When I look at my Users folder, I see folders for the accounts, but some are locked, and using Info, it appears that there's nothing in them.

5. Even after deleting the new accounts (and deleting the deleted accounts from the "deleted accounts" folder), that 20 GB of space is still gone. I've done the migration twice now, and now 40 GB of space has been filled with data I can't seem to locate on my computer.

I've used Migration Assistant repeatedly in the past, and never had any problem. Does anyone have any advice on this?