Windows 7: Share folder over internet and map to drive

Hi everyone,



Consider a company network of computers running Windows 7 Ultimate x64. One of them, named SERV, containing important an important folder (ACCTS) with files that are used for accounting purposes (with Quickbooks Pro 2011).

This software allows multiple users (in the same LAN) to access the same file simultaneously if the permissions are set correctly.

SERV is DMZ through the company router and I can currently make a Remote Desktop Connection from outside the network.

I am trying to find the best way to make this folder available to another computer over the internet securely and to make the other computer (Windows 7 Ultimate x64) able to mount the folder as a network drive.
The end goal: if a copy of Quickbooks Pro 2011 were to be installed on a laptop, and the user is away from the office, the user would be able to access ACCTS on SERV over the internet and use the software as if he were over LAN.

I've spent the past 3:30 hours searching for an answer to this. I've fallen on WebDAV (which Windows 7 is having trouble with?), VPN, and FTP server, none of which I've understood how to setup correctly. Mainly, the trouble is mapping a network drive to the folder and having a relatively secure connection.

Can someone please provide some insight on the situation?

Thank you,

Quicksand10, new to these forums