I believe what GuitarPaul is referring to is that he can see the database folder with mapped drive but not the database server/ db.
The reason you are having this issue not because the laptop cannot see the database server, but because your laptop workgroup login is being rejected by the sql server.
My suggestion is the following
1. Take the laptop to main office and make it join the domain.
Make sure you use it at main office for a day or so, so that it has the security credentials cached in.
2. Then bring back the laptop to remote location, and you should be able to login with your domain credentials(since the password etc is cached).
3. Then connect using VPN (software VPN should be good)
4. When it asks for databases server give it IP address, since name resolution does not work great on VPN(until you have a high end one).
