if you are technologically fluent, here are instructions:
http://www.sticksite.com/tape2cd/index.html
otherwise, here goes. no way is truly free. the cost will be minimal to expensive, depending on the quality and ease for which you want to get to your objective, moving data from cassette to mp3 format.
there are 4 things needed to make a transfer.
1. device to read cassette.
2. way for data to transmit to computer.
3. computer.
4. software to encode raw data into mp3 format.
now they sell devices like these:
http://www.thinkgeek.com/electronics/digital-conversion/85fb/
that will do it all for you! they are about $65, and come with all youll need.
then there is the cheaper way, but not free. understand that quality here will be lost. you will need a tape recorder that has the capacity to transmit sound out, meaning it will need a speaker or headphone jack. you will need to purchase a cable that transmits sound, as in a two ended sound cable, similar to what comes with some flat screen lcd monitors that have built in speakers. you will also need a sound card that has an input jack. some motherboards come with them, especially higher end ones. if you don’t have one, one must be purchased. you will connect the output on the cassette player to the input on the sound card (on-board or through and expansion slot.)
now comes the tricky part. getting the sound recorded. there are plenty of software suites out there, and the ones that really wok well, and can enhance the music to the point where all that was lost int eh transfer is almost reattained cost money.
now my suggestion is, since most of the people here are not technophobes, and these ways are pretty technologically advanced, would be to purchase a device like the Crosley Songwriter (http://www.valleyseek.com/product.action?itemID=21283) which range from about 150 and up. it will move all music, records, lp’s, some even will do 8 tracks. they are really easy to use, and make the process a million times easier.
hope this helps.