Hey! Good news - I've fixed it (with some help from Fubar)
I hate to leave others without a solution so here it is:
I downloaded the PA_Driver.zip/.exe (exe extracted using WinRAR) that you find with a quick google - I used the one that tends to be attached with SonicStage 4.3 (The one with Vista support). Once extracted you can ignore every file except 2, both inside the "Win2000" directory: "SonyUSBF.inf" and it's associated system driver, "SonyUSBF.sys". Move these files to a temporary folder of their own.
Also you will need to COPY (do not move as they are critical Vista files) 4 more files into this temporary folder:
disk.inf from Windows\inf
volume.inf from Windows\inf
volsnap.sys (volume.sys if you cannot find volsnap.sys) from Windows\System32\drivers
disk.sys from Windows\System32\drivers
Now you should have 6 files together - first thing you need to do is to edit "SonyUSBF.inf" in notepad
Locate "[SONYFILT.CopyFiles]" - below this, on a new line, add "SonyUSBF.sys" (alternatively remove the semi-colon from the start of the line containing this filename) - Save and close this file.
Now we edit "disk.inf" in notepad
Locate "[disk_device.NTx86]" and add this line:
%disk_devdesc% = expect_orderly_removal_disk_install, USBSTOR\DiskSONY____ATRAC_HDD_PA____
Save and close that file - now you are ready to install the drivers.
Go into device manager and locate the "ATRAC HD" (which should not being working, hence found under "Unknown Devices"), right click and choose update/install drivers. Then tell Vista you will pick your own and point it towards this folder. It should ask you to confirm a driver install here - say yes.
Once this is installed, another device, a "SONY ATRAC HDD PA USB Device" will be found - again point it towards your folder. As above, confirm the driver install.
Here you might be lucky and get put straight through to the end or it might pickup the Volume "device" in which case, you have to again, point it towards your folder and install the driver here too.
At this stage my device worked ... I still had another "Unknown Device" popup but this didnt have any impact it working so I just ignored it.
Hopefully will work for others that may or may not find this!