You will need a way to get the audio from your stereo to your Mac. Most newer Macs do not have an audio line in, relying on USB for input. The Griffin iMic is a great piece of hardware that has a standard audio line in and a USB out.
Then you will need a cable to go from your stereo to the iMic. The cable you need depends on the diameter of the audio out or headphone jack from your stereo - some of them are 1/8", while older ones are 1/4".
The iMic line in is 1/8". So you will need a cable with one end 1/8" in diameter for the iMic and the other end the same diameter as your audio output or microphone jack.
Then just go to Radio Shack and get a cable with the appropriate sized jacks. They will have them, and they usually cost in the neighborhood of 6-10 bucks.
Searching the Radio Shack website at http://www.radioshack.com/ comes up with these products:
a 6 foot 1/8" to 1/8" cable part number Catalog #: 42-2387 for $4.99 and a 6 foot 1/8" to 1/4" cable Catalog number 42-243 for $4.29.
Connect the line out (headphone jack or audio line out) of your stereo/cassette player to the iMic using the cable bought from Radio Shack, then plug the iMic into a USB port on your machine.
Open WireTap Studio and set the Source menu to the iMic.
Set the file type and saving options.
Cue the source audio and begin recording with WireTap Studio.
You can split the recording into separate songs as you record by pressing the shift key and clicking on the Record Now button at the end of each song.
You can also set WireTap Studio to split the recording on the silence between songs as it records. For more on auto splitting recordings launch WireTap Studio and select WireTap Studio Help from the Help menu. Open the Index and see the section called "Splitting Recordings Automatically".
Or if you prefer to do all of the splitting after the recording has been made the editor can mark silence automatically and then split on markers, or split on markers manually placed. For more on splitting recordings in the editor launch WireTap Studio and select WireTap Studio Help from the Help menu. Open the Index and see the section called "Splitting Recordings in the Editor". For more information on using markers launch WireTap Studio and select WireTap Studio Help from the Help menu. Open the Index and see the section called "Using Markers".