Hello,
There are a few ways you can do this.
As Lexluethar said, you could just enable file sharing in Windows XP (assuming you have XP) share the files on your laptop and access them over the network from your desktop PC.
The best way would be to use iTunes. iTunes allows you to share music libraries over a LAN with other iTunes users. Similarly, Winamp and Windows Media Player also allow you to share music over a LAN. Note that you need to be using the same media player on each computer (i.e: iTunes <---> iTunes).