I have NO idea what router to buy

Okay, my first supposition is that the cable modem considers "itself" to be an internet device. So you have two approaches: either use the cable modems "address" or have your own, provided automatically by your cable provider. Usually it is the latter with your computer getting it's own address provided by dynamic addressing from the provider.
If you are using dynamic addressing (DHCP) with your computer, which you can confirm with your cable provider, really all you need is a wireless router of the type you can buy commonly.
You should probably buy one that uses the "N" series of speed enhancements, even though you may have to "throttle it down" if your wireless equipment in your computer only supports the lower standards (such as "G"). If you are buying all the pieces at once, make sure they match. Staying in the same brand will usually simplify matters during set up. If your computer doesn't have wireless now, there are two choices, USB connected which uses one of your USB ports to connect to the computer or an internal card installed within the chassis of your machine if it is a desktop.
If you have a laptop, you can't do the internal card, but you can install an "expansion card" in the expansion slot on your laptop. You will need to take the laptop to the store to make sure you get the correct card. It sounds like you have built in wireless on your machine and the number (802.11) gives us the series of wireless speeds that it can support, although there is a letter that is missing. However, at this point, it probably makes more sense to get an "N" series router in any case, as any new equipment you add will support it and it will still work fine with the older "G" standard. Understand, however, if you mix old and new the connection speed will step-down to the slower speed for all devices using the router, so don't put any "G" devices on an "N" network if you can help it.
Setting up most wireless routers go either one of two ways: the installer works or you have to call tech support to finish it. It seems like those are the only choices. However, the companies seem to understand this and support for a common installation problem seems to be both available and knowledgeable on this piece of equipment, unlike so many other 'puter pieces you can buy. I have heard every brand held up as the worst and touted as the best, so I can't tell you which way to go on that, although I would avoid store-brand products and stay with a company who makes this stuff themselves, more or less. (Netgear, Belkin, D-Link, LinkSys are common brands.) Just make sure if the install doesn't work and you can't quickly figure why, don't be embarrassed to call tech support. It seems like they expect it.
These devices can be hampered by : -distance from card to router (150 ft is generous and not typical) -stuff in-between the card and the router (Like a garage with lotsa metal stuff in it) -other electrical devices, such as microwave ovens or cordless phones. Both would only affect your connection while they are specifically working (ie: ON) -some A/V equipment, but not as commonly
I would say "go for it." Take your laptop(?) to the store, get good quality hardware (not no-name or store-brand) and give it a shot. You may end up calling tech support (I did) but it isn't as big a deal to do that as you might presume.) In the end, you will likely be able to do it, with a little guidance.
If you want to hook up a number of computers to cable, you either need to go with the cable companies plan to account for each one (and a fee?) or possibly an "internet router" that acts like it is a single computer (even though it is just a hub/router/switch box) and allows the computers to share the connection like you only have one computer on the cable co. box. It works but , as you would expect, is a little more setup, considering that you have a box pretending to be a computer and then parcelling out data to several computers via a wireless connection. It's more complicated.
Short answer: Try it yourself. You can always call a service if you hit a brick wall, anyhow.

Since those look like callsigns in your ID, you must be west of the Mississippi :-) Start by going to a Staples store and buying the Linksys or Netgear wireless routher that is probably on sale for about $40. I prefer Netgear because it does some tracking, I sell it, and I'm more familiar with it, but that may not be an issue for you.

If your computer is set up 1:1 with the network card plugged into the Comcast modem, you're probably going to have to "clone" your computer's MAC address into the router (that's why I suggested Netgear, I know how to do that :-)

You will basically take the router out of the box, read your network attributes on the working PC, which is probably Obtain DHCP automatically, do a START/RUN/CMD enter on the working PC, and then type IPCONFIG /ALL on the command line and read all the information given. Note the IP ADDRESS your PC was given and the DNS server addresses. You might take the time to copy down the 12 HEX digit (seperated by -) MAC address of the LAN card.

Now, in the Netgear, you can follow the quick setup, and tell it to clone the network card for your desktop, so when you plug in the router it still looks like your PC is connected to Comcast!!

That's about all there is to it. You turn on wireless and security, set the type of protection you want, give it a password, give the router a password and you're good to go. Plug the router into the modem, the desktop into the router, and look for the wireless network on the laptop. Send it your security code, and save the settings (connect automatically is good), and you should be done.

Carl