MIDI cannot record audio - it is a data-only protocol designed to allow instruments from different manufacturers to talk to each other.

Althougha separate audio device is a good recommendation, how about trying to use you existing set-up? Most computrs come with a sound card built in. Admittedly the input sockets are usually 3.5mm, but are usually stereo. Check what type of connector you have. If it is a 3.5mm stereo LINE input (this is important - it cannot be a mic input), then something like this will suffice:

http://www.amazon.co.uk/3-5mm-Stereo-6-35mm-Audio-Cable/dp/B0034DSUMK

The black jack goes to the Pod left output and the red to the right, the 3.5 into your line input on your audio card. Your audio card may have different connectors or no line input, so a separate solution as recommended by the second guy may be the best way to go.

If you want to sing at the same time then you will definitely need a more sophisticated audio device than what is built into your computer, even that Fast Track will only allow you to record your mic and one (left/mono) output of the Pod - if you want the Pod in stereo and also be able to record your mic you will need at least three inputs (so you'll probably need to look at a device with four inputs).