I'm trying to pair my iPod Touch (or iPhone) to the PC, to use the PC as the speakers. I know that Windows Vista's bluetooth doesn't work as a A2DP by default (right?). Is there a way to do this?
You can try different Bluetooth stacks, however what you can use really depends on the Bluetooth chip in your pc.
I can not guarantee them and you have to be careful as they use drivers that have the ability to mess up your computer - I had endless problems with a old version of Blue Soleil, but their new version worked perfectly.
Some of these are a lot better than others. Also, some are free and are licensed to the manufacturer of your bluetooth chip, so you may have luck installing whilst others may require you to pay. For example, in my laptop, I can use blue Soleil or Toshiba, where as if I install Blue Soleil on another laptop, it only works in demo mode and prompts to pay.
Edit - I have seen AD2P as a option for many of the stacks, however I cannot guarantee what direction. Though, if anything can do it, installing a different stack would be your best bet.