Connecting multiple offices

I have four offices spread over the state with different ISP's.  I need to get them on the same network so they can all share files from a server in one location.  I have fairly extensive LAN knowledge but WAN knowledge is very minimal.  What do I need to get these connect with the least amount of cost/setup yet something reliable?  The offices are all connected a little bit differently.  Three have standard cable/dsl setups but one of them is piggybacking off of a T1 that is in the office complex I believe.  Thanks for your assistance.  
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Rob HutchinsonDesktop SupportCommented:
I can give you some general info that might be of some help, or not.

You have four seperate networks in each of the four offices since these offices do not share a common network( which is what you want) you need to create a common network to connect all four offices.

What will happen here, is you will pick one location( where the server is possibly) as the location where the other remote locations will VPN into. The VPN connection among the four locations will likely be connected all the time and require someone with VPN's/routing to configure it all.

To make life easier, you might want to look for a company with remote server hosting which, at the same time, gives remote server login ability that can be setup. This way it's easier as all four locations would connect to the remote server without having to setup any special routing config among the our netorks and use their existing connection.

Deciding on which option is best depends on the budget, the number of users involved, as well as the applications being shared.
You need make one of the sites the main site, preferrably one that hosts all the servers. Next:
1. Make sure all ISP connections use a static IP address. If not order/switch to one you cannot configure VPN without this.
2. Purchase a VPN concentrator for the main office.
3. Purchase VPN appliances for the remote offices.
I have only used Cisco VPN concentrators.  Your best best would be to get a PIX501e for the main office and a some 3Coms for the other offices:
Not sure if 3Com makes a new version of these, but they are easy to setup and maintain:
From there you will need to research how to configure IPSEC VPN tunnels, preferrably using AES encryption with MD5 hash algorithm.  

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Kerberos24Author Commented:
Thank you very much.  Going to research VPN concentrators.  
You may also look into Cisco's DMVPN feature in IOS 12.4

It is the closest to a perfect solution as you can get.  In your situation where you're dealing with dynamic IP addresses on the branch offices, DMVPN will not require you to incur additional cost of getting Static IPs at your branches.
Also, if you already have existing Cisco routers at both your main site and branch offices, you can leverage that hardware (assuming they can support 12.4)
here is a link to this feature:

I hope this helps.
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