You'll need a driver that supports bluetooth A2DP on the Windows 7 machine. There are drivers for bluetooth the transport layer and then there are drivers for the bluetooth audio profile support. They are separate.
Windows 7 came with no A2DP support and MS asked bluetooth hardware manufacturer to add this feature in driver upgrade. All bluetooth hardware on laptop where most of the time we need A2DP are made by Broadcomm (widcomm software), Toshiba or CSR. The last 2 manufacturer seem to have A2DP in Vista which should work in W7 but for Broadcomm nothing around.
I recently purchased something called an Aircable Host XR - a USB-connected bluetooth transmitter - for use on a win-xp system. It came with absolutely zero software (no CD, no drivers, etc). There apparently is no drivers needed when connecting it to an XP system.
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