Heh, that "linksys" stuff. LinkSys is a company, albeit a very good company IMO. Its what they make, wireless routers, is what you are thinking about. Wireless routers take the cable or dsl line from the wall and take the signal coming from those lines and broadcast it, generally in an area big enough for a medium sized house. That signal then is picked up by wireless adapters, wireless cards and electronics with those devices built into them, i.e. some new laptops, palm pilots, and the DS. Basically, what this means is no more LAN wires.
Blue tooth is similar I suppose, but it doesn't connect to the internet really. It creates a "home network" or intranet. (not INTERnet). Basically, all bluetooth devices take in and send signals to other bluetooth compatible devices in a given area automatically.
Its kind of hard to explain in a non-tech way, but I tried.
-Blue