I have 3 computers networked here at my business. Internet connection comes in to a router, then to a network switch, then to the cpu's. I have another location(miles away) I want to add that computer to this network. Is this possible?

sure its possible. usual way is to create a hardware vpn tunnel between the vpn capable router at that end and the one at your end. This creates a secure tunnel between sites. Imagine the power of knowing how to internet search http://www.lib.berkeley.edu/Teachin...

Depends on how you wish to use the network would be more of a question as well as speed. If you just need a few files off the office then there are plenty of ways. I like a program on softpedia called barracudadrive. It uses https. If you need microsoft file sharing then you need a vpn that can support that protocol. Not all do easily. Phone lines could also be used. Kind of expensive usually. Ties up a line. There are also wireless line of sight products. Might even have a way to run fiber depending on local rules. Some places allow an easement on a first come basis like New York city. "Best Practices", Event viewer, host file, perfmon, are in my top 10