Detailed Instructions on Setting up a VPN?

Bit of a network newb and was wondering if somebody could point me in the direction of any good guides or give some detailed information on what I need to do here. Basically, we have the Xserve setup to store all our files where users can go in and take files, edit them, and then update them. We want this ability to also be available for our employees when they're away from the office at home.

Like I said, I'm new to setting up VPNs, port forwarding, firewalls, etc. So as many details as possible helps.

We have a Sonicwall already setup here and users are on both Macs and PCs.