If you can't set up a direct link between your LAN and the remote site, then a VPN is your best option. You can set it up basically in two ways:
- Have the server establish it.
- Use a site-to-site VPN.
In the first scenario, your server will establish the VPN using its RRAS service; it will be the only computer that will be able to talk to your network. You shold use RRAS instead of a standard user-space VPN connection because otherwise that would require a user to log in and activate the connection in order for it to work; RRAS will handle that automatically.
In the second scenario, you'll have a router/firewall at the remote site establish a VPN connection to your network; this will let many computers at once talk with it, and it is normally preferred because it's more reliable, manageable and secure than having single systems doing that.
In both scenarios, you'll need a VPN server in your main network; this can be a router, a firewall, a Windows server running RRAS or ISA/TMG... almost anything you want; it could also be your current firewall, if it supports VPN connections.
L2TP/IPSec VPNs are usually more secure and reliable than PPTP ones.