Yep. That did it.
It turns out that the ASUS update needs the drive to be in emulated IDE mode before it’ll update. I suppose that makes sense if ASUS are lazy useless fools who expect me to use a SATA drive on an emulated interface in order to update it because they’re too inept to produce flashing software that works on the drive in it’s native mode. [/rant] Aaah.
Anyway. I strongly suggest that anyone finding this thread tries this solution, it works like a charm. However, it worked for me in Vista. F****** about with AHCI and IDE in XP can cause bluescreens and all sorts of woe, so be careful.
In addition you should WAIT when you do it after you reboot, because Vista will spend quite some time finding and installing drivers for your “new” drives. (As far as Vista is concerned the old drives are gone, and new drives have arrived). Because if Vista turns off a drive, to install the driver and it’s in mid firmware patch then the drive may well be forever useless.
Finally it’d be desirable to first create a simple Windows boot CD, stick the firmware update on the boot CD, power down and disconnect the hard drives before switching to IDE from AHCI mode, booting from the CD, flashing, powering down, and switching back to AHCI mode before reconnecting the drives. The two reasons for this are to avoid any blue screen woes, and also to prevent extra redundant (but offering no redundancy) drivers being installed, which is usually harmless, but never desierable.
Edit : Sorry, it’s rather rude of me not to say thanks!