unfortunately, it doesnt really work that way ( or at least i havnt figured it out then yet)
the only way I know how to hook up a guitar or bass to the pc is when you use a GuitarPort. as far as i know a guitar gets its feed trough the cable.. so it would drain the power from the Mic or line-in port from your pc,.. and im not sure if they can deliver the ammount of power needed.
like said, As far as i know.. I could be wrong ofcourse.