I think most sound cards have a "mic" input at the back.

Here's how I hook up my guitar to my computer:

All you need is a regular stereo cord (the jacks on either end should be the same as on a set of headphones for your walkman - the small jacks).

Then I get my trusty stereo to phono(?) adapter. Basically, you plug a small stereo jack into it, and then the other end of it is a plug the same size as your regular patch cord.

The phono end of the cord now goes into your guitar, and the small stereo end goes into the mic input in your sound card.

Hope that helps, and if it's confusing, just say so and I'll try to clear it up.

Oh, and also, in your volume control settings, turn down the input volume of the microphone from max, or else you'll just get a distorted guitar.

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ok, i'm not really the eggman