LP Recorder from CFB Software in Oz is excellent for digitally recording vinyl LPs and tapes. Inexpensive, easy to use, no frills and gets the job done.
If you like you can use LP Ripper to split vinyl LP or tape recordings into tracks to make CDs or MP3 files.
See
http://www.cfbsoftware.com/default.htm
If you want to go the freeware route and need an MP3 encoder
consider Tord Jansson's BladeEnc -
http://bladeenc.mp3.no/ - fast and effective. It's a somewhat unintuitive command-line application, so it's handy that various people have written assorted frontends for it.
Of the various frontends available I recommend Holger Dors' Razorblade -
http://www.dors.de/razorblade/ - also excellent.
Install BladeEnc, install RazorBlade and off you go.
Presumably you have a line-in on your PC or soundcard to feed the line-out from your cassette player.
Happy listening!
Mac