I can only try:: alot of what you said is true. the reason i didnt say to use ad-aware, is because i have found it to be utterly useless. spybot may not be able to get rid of what it finds totally, but at least it finds the stuff. ad aware doesnt FIND alot of things. it also jams up alot of memory with all its graphics. spybot is light sweet and gets the job done.
as for wireless cards, it is no simple process to install a wireless card. (getting a hold of a wireless broadband card, those offered from cell companies is highly unlikely, unless they borrow it from someone, as the bill must go somewhere.) a wireless card that would attach to your router will need to have an antenna. the person using the computer would also need the pass-code. not only that, but you can also limit the router to only certain MAC addresses. this is an address that the IEEE gives out to manufacturers. no 2 are alike (supposedly). yes the mac address could be spoofed, but i doubt a typical yeshiva kid could figure out how to do it. and again, they would still need the pass-code.
as for wep vs wpa, go wpa if you can. not all routers have wpa. try to get one that does. i think all linksys ones do, and they are really easy to setup. as for someone getting into your computer via the wireless router, that would take heavy duty equipment and skills. unless your storing documents of high value, and you are a high value target, i wouldnt lose sleep over it.