Well if inside servers need to access computers on the outside network that are not behind a firewall then by default netbios connections from the inside would go out and connect to remote computers and the pix would recognize it as an established connection and permit it through. But if outside pc's need to connect to servers on the inside network then you will need to either open up the netbios ports 137,135,139. That would mean anyone could connect to them as well. If you can handle the administration and know the ip's of the outside pc's. You could set up access lists to allow only those pc's.
Just so you know, the pix offers free 56bit encryption. So all you would need is the VPN client.
