I assume the 4-track cassette has a little mixer on it or some way to sum the tracks together. If your computer has a decent sound card you can find a decent audio program that you can record directly into from your 4 track. There are so many programs and differences in opinion about whice is best for the price. I'd say to find a free one to start with.
Once your audio is in a program you can convert it to mp3 and mail it to people. You can also edit, EQ, etc. If the program has multi-tracks and editing you can sell the 4-track.
In a noisy room direct recording is best. Like a POD or some
amp modeler. Speaker emulators are also available to help your tone if going directly out of an amp.