If its a digital cruise control signal then its a little harder to interface with. You need to figure out the sequences etc. Not worth the hassle.
If its analogue (resistive ladder) then its definitely possible to interface the controls to your PC, but I wouldnt recommend it. The idea of linking accellerator and music player controls just doesnt feel right IMO.
As was stated above, a separate (or factory integrated) controller would be better.