There is the bluetooth A2DP profile. That can function as a sort of line in.
Why don't headphones won't work for you?
Also, if your phone has a mass media storage mode, getting a synch cable would let you play music files from the phone using a media player on your laptop.
And surely you have Microsoft Media player? If you don't think you do, what happens if you do a Start->Run mplayer2 ?