I have a client that has a single install outside of her network installation. I need to migrate the users with their passwords into the network installation. I've tried backupbuddy but it seems to skip the users. Any idea how I could pull this off manually?
Normally BackupBuddy should transfer users just fine, it might be issue with importing into multisite installation. Have you tried asking developers about it?
As for more hands-on approach I'd try creating users in network and then overwrite hashes of their passwords in database with values from original installation.