From my (limited) experience, a 10Mb card is only just up to network gaming. I'd go for a 100Mb card - or USB network connection. They're more expensive, but the latency you get from 10Mb cards can be really annoying.
To get a LAN going, you need a crossover cable to connect the NICs - not just any RJ45 cable. Any decent electronics store will sell these.
You also need a protocol on each PC. A protocol is a set of rules that allow the NICs to "talk" to each other, but has come to mean a suite of utilities, such as TCP/IP.
For most LAN gaming, TCP/IP is what you need, and Microsoft supply their own version with Windows. If you've got a modem, it's probably installed already.
If not, it's really easy to install - when you install the NIC, Windows will ask you to configure it with a protocol.
Use a private IP address, from 192.168.1.x, where x is any number you like. I tend to start at 20 and work up, but that comes from working for corporations where numbers below 20 on a subnet are reserved for printers and routers.
It's not important what 'x' is, and you won't need to configure DNS, WINS or anything else, except the subnet mask. Make that 255.255.255.0.
If you're on the internet, don't enable File Sharing, - it's a massive security hole.
If you need any more help setting up your network, post back.
I hope this helps
