I work for a drafting business that has 2 locations...one in Ga and one in Al...here in Ga, our communications provider is Comcast...in Al its Brighthouse...We work mainly with autocad and .dwg files.... for the past 10 years or so we have operated on 2 separate servers. All is well when we are working on 2 separate jobs but the problem comes in when we are working on the same job. Files get overwritten and lost because there will be a file that I am working on in Ga, meanwhile someone ells is working on the same file in Al...when they get done with whatever they are doing with it they will e-mail it over here and whoever receives the e-mail will overwrite the file that is on our server, assuming that the one being e-mailed is the most updated one… and bam!! I lost all my work....that is just a simple example of the kinds of issues we run into using 2 servers...its actually more complicated. About a year ago we decided to try and fix it...we had a company based out of peachtree city come in and set us up with a sonicwall router with VPN in each location and set up a "tunnel" between the 2 locations. Ga has the server that both Ga and Al view and edit their files from. It's not working as planned...first off it's slow as crap to access the Ga server from Al through the "tunnel" … 2nd of all, Al has to copy from the Ga server and paste on their computer, work on the file then cut and paste back to the Ga server which leads us right back to where we started (overwritten files and such) just with a slower process so we are kinda worse off than we were to begin with. I am wondering if there is a way to make the "tunnel" a lot faster and a way to ENABLE Al to open a .dwg file directly from the Ga server and work on it on their computer and be able to edit and save just as if they were working at the office in Ga....I know that was a ton of info and it’s a very complicated , confusing situation...but I keep telling myself that we can't be the only business in the world that encounters this problem and there must be a good solution...If you are able to help us out, it would greatly increase our efficiency and everyone here and in our Al office would love you. Please help!!It would seem that you have already identified your problem.
The problem is having two servers.

Withe the proper software, a user has to "check out" a file in order to change it. This requires there be only one copy available for your work. Any other copy can only be an archive and should not be used for updates until there is agreement that the all changes up to a certain point are valid.
VPN is very appropriate for your work. But there still be the restriction that a job be on only one server has to be kept.

There are special programs that DEAL with this issue of several users working on the same data set. But it requires the data set be broken down into small chunks. With CAD files that can be a challenge. That would mean a drawing would have to be in sections that later can be automatically merged into the whole. If you work has not already been organized that way, you have a job before you.
Why not have everybody just use one server? Thee are companies that will rent virtual servers at reasonable prices and offer very good redundant fail safe systems.
For a startling point, why not chat with these people:
http://www.rackspace.com
You could ask if the "Cloud Hosting" thing would work for you.
Of course, many others offer this service. Pick their brain and then you will know what questions to ask when you talk to one of their competitors.

(Pardon my grammar, this is just a quick ANSWER.)One more option is to find out about a using a Citrix sever.
http://www.citrix.com/lang/English/home.asp

We use this method to share files and folders, Across several cities, county's and states with a good security connection.