okay this is weird. I thought I'd try something different:
I put the original drive back in;
installed Paragon Partition Manager;
made the partitions smaller by deleting the "storage" partition (which was empty), deleting the "recovery" partition, deleting as much stuff as possible, then shrinking the remaining "OS" partition to eliminate all the free space;
Restarted and booted the Norton Ghost CD;
Ghosted from the original drive to the SSD;
of course it didn't boot because the boot.ini (or equivalent) would have been stored on the "recovery" partition, which was the first partition on the drive, so I put in the Windows 7 DVD and went through the options to fix the startup, where it detects your Windows 7 OS and creates / fixes your Boot.ini.
So now it works, but it's still the standard bloated OS that comes with your average Asus laptop, utterly dripping with fat and free trials and superfluous applications.
So I tried booting windows from a USB disk (again). I tried this before and it didn't detect the SSD, but this time I formatted the USB disk accidentally, forgetting that I already had the Windows 7 install disc on it (perhaps I formatted it in NTFS this time, instead of FAT32?) and now it detects.
yay.

(finally!)
so...I'm not sure which part actually made it detect!