This afternoon I was messing around with the Bluetooth on my iPod Touch and discovered how to stream music directly to my PC over Bluetooth. The sound quality's pretty average, but listenable. Good for parties, so guests can play their music from their iPod. I'm using Windows Vista, so I'm not sure if it'll work with XP or Windows 7. Here are the steps:
1). Turn Bluetooth on on your iPhone/iPod Touch by going to settings, general, Bluetooth. 
2). Pair your iDevice with the PC by going to Bluetooth Devices on your PC, then go to Add Wireless Device. Go to Bluetooth on your iDevice, and let it search for devices. On your PC your iDevice should appear, then double click it to add it as a device. On my PC it asked me to install driver software, just go cancel if this happens.
3). Go back to Bluetooth Devices. Your iDevice should be listed, with a speaker and musical note for its icon. 
4). Go to Bluetooth Settings in the menu bar above the devices. 
5). Go to the Audio tab. Double click on your iDevice to connect to it. You don't have to be in the Bluetooth settings on tour iDevice for your PC to connect. 
6). Once your PC is connected to your iDevice, play a song on it. The song should stream to your computer and play.
7). You can pause, and skip songs on your iDevice, but volume has to be changed on your PC. 

Note: I was using a 2nd Generation iPod Touch running iPhone OS 3.0. The 1st Generation iPod Touch and iPhone do not support Bluetooth. I was also using a PC running Windows Vista Service Pack 2. The Bluetooth interface is slightly different on Service Pack 1. 
Note: Sorry for my excessive use of the word 'iDevice', It's easier to refer to devices running iPhone OS as one thing, rather than saying 'iPhone/iPod Touch'.