VPN software

I am needing to set up a VPN for my small-medium buisness. We’re running a Windows Server 2003 server, with only on NIC (we’ve got a hardware firewall.) I’m having trouble setting up the windows server VPN (I think it might require 2 NICs with the server bridging the intranet to the internet?) so I’m looking to try out other solutions. I’d like to try not to spend tons of money on this, but I really need to let my remote workers access files on our server.

Thanks!
-Eric