HELP!? Can't access SD card from Windows 7 (64-bit)

[Guest jamesyuk]

Hi, when I connect my San Francisco to my netbook running Windows 7 32-bit, it detectes the 'phone properly and I can access it as a mass storage device. However, when I connect the 'phone to my desktop PC running Windows 7 64-bit, it appears in device manager as an ADB device, but I can't access the SD card via mass storage. No mass storage device appears, no drive letter is assigned, etc.

Any ideas? I'm getting really stuck. I've tried unplugging all USB devices, booting up and plugging back in again. I've tried different cables, installing various drivers found here on the forum but all to no avail.