I have been using two great tools to learn and practise tunes using the computer. The first one is a site called Practice Studio. There are a lot of MIDI files that play tunes at different speeds. These files are three types. One has the melody and rhythm. One has the melody line only and the third just has the rhythm. By playing the melody MIDI file tunes a can be learned and then after learned intonation can be checked. After the melody is learned, the rhythm MIDI can be played and you can play along Karaoke style. This is great for practicing beat. I have downloaded the MIDI file and converted them to mp3s and burned them onto a CD for easy playback. It is best to start on the slow speeds. Even after being able to play the faster speeds it is good to practise at the slower speed and constantly try to improve intonation and beat. Remember, first you get good, then you get fast. It does not happen the other way around.
Another tool is a freeware program called Audacity. Audacity allows you to load a sound file and crop it down to the part interested in. Audacity also can slow down a tune while still keeping the pitch. This is great for learning tune from a CD.
You will need a program like Music Match Jukebox to rip a tune from your CD to Mp3 format. If you want Audacity to edit a MIDI file, a MIDI to MP3 converter will have to be used.