you dont,cant, wont...
The connection part is straightforward: put a stereo cable between the headset jacks on the cassette player and the microphone jack on the laptop. Buy an adapter cable from an electronics store for that job. Now about the software to "read" the music... That needs more research. Sorry. Reask your question ... Something like "What software allows copying audio from the mike input into files on a laptop? "
Hold down ESC while turning on via POWER button. The hit F1 when screen message tells you to do so!
Well, you can certainly password each of the computers seperately. But the router will only accept one password so all 8 laptops will need to use the same password to log online.
The cheapest laptop brands are Acer and HP. Both of these brands have high quality laptops for under 200 dollars USD. They are both long lasting and typically come with fair warranties and good customer support.