I have used Edimax 802.11g cards before and found them very cheap but easy to set up and good signal strength (helped by an aerial on a cble rather than tcked behind the machine). Seehttp://www.edimax.co...1_id=1&pl2_id=44
If you need 802.11n they also produce:http://www.edimax.co...1_id=1&pl2_id=44
which I haven't used but is pretty good value for an n card.
Amazon sell their stuff.
I don't know about Linux compatibility - I just know the few times I tried Linux it was almost impossible to get wireless working (with a whole bunch of Netgear, LinkSys and other PCI cards).
They say http://www.edimax.co...1_id=1&pl2_id=44
is Linux compatible but only with kernels 2.4/2.6. That probably means that was all it was tested with.
PS If you can afford to go for WiFi-n then you will find it is much faster (up to nearly 6 times) for file transfers between machines and I suspect if you have a lot of people trying to access a broadband connection at the same time the increased bandwidth would speed that up too. The best thing about WiFi-n is the improved range and signal strength.
If they are all in the same 'classroom' it would be cheaper to buy a bunch of wires and have a wired network and then you don't have to worry about compatability with Linux too much. Not as neat but cheaper, a lot less hassle and if the machines/router have gigabit interfaces very fast.