Dean - there is one thought I would add to Iceman's excellent overview. Does your network have any security right now? If you have a cable modem and are staying connected to the network 24/7 many people will say that it is *very* important that you have some sort of firewall to prevent any sort of hacking into your systems. Some people are relying on features of Windows XP that act as a software firewall, but I don't know if I would trust Microsoft for my security. They couldn't even manage to protect their own servers from a security threat posted last year (that virus that hit two weeks ago)!
If you do not have any security currently, an easy way to add some while also providing the wireless connection you want is to buy a Wireless gateway (also referred to as a router) instead of buying a plain, vanilla wireless access point. The router will connect to your cable modem and act as a firewall preventing access to your network. It will also act as a wireless access point allowing you to share your network resources (and the Internet of course) via wireless cards. You can kill two birds with one stone. Since you already have at least one other computer near your cable modem, you should buy a router that has both wireless ability and standard, ethernet network ports. This type of thing may not protect you from a determined attack on your system, but it will be the same as putting a decent lock on your front door. Most hackers (and bored kids) will just bypass your network and move on to the next one "down the block" that has left the door wide open. Keep in mind that hackers don't set out to break into "Dean's computer" but rather they use automated tools that look for vulnerable networks. I see that my computer is constantly being probed by these tools from all over the world (right down the street all the way to Russia and Brazil).
The router that I use (and have been happy with) is the DI-713P from DLink. You can get it online at Amazon or at stores like Best Buy and Circuit City. There are lots of different brands that do the same thing, all at various prices ranging from $100 on up. Here is a link to a site that reviews the different wireless networking components and has some decent information:
http://www.practicallynetworked.com
Here is a link to a site that does a great job of talking about security and putting it into terms that even my mother understood.
https://grc.com/x/ne.dll?bh0bkyd2
Good luck,
J