I currently have two computers plugged in to a router, which is plugged in to a cable modem. This way they share an internet connection. I will be getting a new (laptop) computer sometime soon, and I would like it to share the internet connection wirelessly, but I also would like to be able to share files, the printer etc. with one of the desktop computers. Would it be possible to simply plug a wireless router into the current one and do this, or would I need something like this? It seems like the latter is a simpler solution, but it is much more expensive for some reason.
I opted to replace my existing router with a wireless one. It’s a 802.11b but works fine with the 802.11g laptop I just bought. I’ve seen the Linksys WRT54G router for $80 in several places which is the same cost as that access point you linked to. Fewer wires if you have a single device connected to your cable modem rather than daisy chaining an access point to the existing router plus you have a spare wired router as backup.
Networking is just the same as wired as far as sharing goes. You will of course want to enable authentication so people don’t hitch a free ride on your broadband connection.
I had considered doing that, but the cost of wireless adapters for the two desktop computers and the router adds up to about the same or more than the access point.
Most of the wireless routers also have standard wired ethernet switches built into them. The previously mentioned Linksys WRT54G, for example, has a 4 port ethernet switch built in.
So if you went with a wireless router, you wouldn’t need to switch everything to wireless, you’d be able to plug your current two computers in the same way they’re currently connected.
However, if you’ve already got a router, a wireless access point would really be all you need.
Sorry if I didn’t make that clear. I’m using a similar D-link wireless router that also has four wired ports so I didn’t have to change my desktop machines. I should have said no extra wires if you replace the router instead of just adding an access point.
FWIW todays Fry’s ad has a D-link USB wireless adapter for $10 after rebate. I think it’s an 802.11b but that’s still faster than cable modem bandwidth so I don’t see it as a drawback.
Excellent, that’s what I needed to know. 
Most new laptops contain the wireless adaptor built in. You can run that wireless router through your current one but there is no need because they all have wired ports. I like the D-Link routers with the print server built in because then you can print from any machine through the router that is connected to the computer. They provide the software which is easy to use and works great. I have a DI-704P.