OK, a router can be used to share either a (cable modem) or DSL broadband connection. The only difference is, if you use the router with DSL, then the PPPOE information needs to be programmed into the router. If you use the router with a cable modem, then it's not likely that you'd have to enter any information into the router to get it to work OK. At worst, you might have to enter a MAC address for it to "spoof".
The wireless bit is a whole other story. The wireless connection needs to be set up in the wireless access point (or router). The wireless connection also needs to be set up on each computer that will use it.
You are in luck, as buy.com has a Belkin brand wireless "g" broadband sharing router on sale for thirty bucks at the moment, and free shipping.For the wireless access cards for each computer, you CAN use a USB adapter, but I would strongly suggest that you do NOT use one. The reason is that USB is rather a slow interface. It will be a bottleneck. A better idea would be to get a PCI format wireless access card for each computer. If a notebook, get a cardbus style wireless access card. The access cards you use with each computer do not have to be any specific brand. However, I've had good luck with Belkin brand. So the following would be a good match for a Belkin brand (or any other brand) router. I use Belkin brand access cards with a Netgear WGR614 wireless "g" router, by the way. Note that these access cards are also on sale for about thirty bucks, free shipping. -Dave