Okie-dokie, let me explain:
EDGE is a fancy system that Cingular has started adding to their cell towers. It has a lot more capabilities in terms of what it can transmit and how fast it can do it, but it isn't nearly as widely used as GPRS. GPRS, on the other hand, is a bit slower -- roughly 1.5x the speed of dialup, not counting the ping times -- but is very widely used now.
If you're going to use the wireless connection in only one spot you could go with the EDGE card, provided you have coverage there. However, given the picky nature of cell phone towers you might want to get an EDGE/GPRS card just in case one or the other goes down for a while.
If you already have an account with Cingular, particularly a Family Talk plan, it will likely be cheaper to add on another phone -- one that is EDGE and bluetooth enabled -- and an unlimited data transfer plan. I know on my phone the unlimited data plan was only $20/mo, despite the fact that the website lists no such plan on it. Go in to the store and talk to a Cingular rep just to be sure you can't beat the $60/mo charge for EDGE/GPRS broadband access. If you can get it cheaper invest in a bluetooth card or USB adaptor -- I've seen 'em for $10 or so online -- and you can use bluetooth to connect to the phone, using it as a modem.
Now as far as connecting up the network, you have a few options:
1) Simple method: Install the Cingular card on one system in the house and configure it to use Internet Connection Sharing. The downside of this is that you have to manually configure the IPs of each computer or device on the network -- no DHCP is offered -- and make sure they all use 192.168.0.1 as the default gateway. You'll also be unable to set up anything like port forwarding or the like, which could make using your broadband to the full extent tricky for anybody not on the "main" computer.
2) Somewhat more complex method: aquire a server OS and a vaguely decent computer or laptop. (Since the Cingular card will be PCMCIA) The only issue I can forsee would be finding drivers for Server 2k3 if you go the Windows route, so try using Server 2k instead. (or better yet, some build of Linux if you can find drivers for the card you're using) The tricky part will be configuring the server OS properly, but you'll be able to set up things like a DHCP server and port forwarding, which will make things much easier for every other computer on the network.
Now there are a bunch of details I left out -- a lot of details, don't want to type 'em up for one plan if you aren't going to use it -- but once you pick one I can walk you through it. Regardless of which way you decide to go you'll either need to use a laptop as the "connection server" or you'll have to purchase a PCMCIA drive or adaptor. (Unless you wind up doing it through a phone)
I also HIGHLY recommend asking specific questions about whether or not the Cingular cards can be used such that you can network them. Certain ones may have issues if they require special software to connect, etc.; remember, these were primarily designed for business executives on the go.
Good luck with it. Let me know if you need help; I'm glad to assist you, as I'm quite curious to see how successful this is.