How do I get stuff from a home audio cassette (remember them) to my computer in .wav format?

What kind of sound card inputs you got? I have a Soundblaster Live Platinum 5.1 which has a box that fits in one of my front drive bays and has a ton of input/output connectors that you could easily plug a cassette player into.

just speakers out and microphone in.

get one of those speaker connnecors that come with most pc speakers, or at Radio Shack, <2-RCA male to 1/8" stereo> and plug it into the "line in" of yer soundcard, adjust the audio level using the sound mixer in windows and yer done, and yes, it's easy as that !