Well heres how i do it.

I can do it one of two ways.

You have to buy an 1/8 in jack so you can plug your guitar cord into it...and then you plug that into the back of your computer. *the microphone outlet

If you already have a dig mic installed...then you can go to "Start" on your computer....then "all programs" then find..."accessories" ...then..."entertainment" then click on "Sound recorder" if you have it

Granted neither of these give you top notch studio recording...but you can record your ideas.

*I missed a lot of info so people can add on to it*