Do they all access the PC with the same logon?
If not - Re-install 6.5 for multiuser and copy their ID/Names/Desktop to the appropriate directory (C:\docs & settings\user\etc...)
When they launch Notes, it will then only read only the ID from that folder, and they can have a custom desktop/address book etc...
Make sure you install it with a 6.5.* client only CD. The ones with the Admin and Designer clients do not have a prompt for multi user install