OK, here are some other things I've tried.
I checked the jumper setting on the drive - the default is SATA 1.5 Gb/s so that should be fine with my motherboard.
Maxtor's website says that no drivers are necessary (and they don't have any to download on their site) because their drives are designed to use the generic drivers.
Whenever I shutdown and try to start again I get two outcomes which alternate: the computer either starts normally, with a beep, checks memory, and tries to boot from the XP CD; or it doesn't beep and gives the following:
'VIA Technologies, Inc. VIA VT8237 Serial ATA RAID BIOS Setting Utility V2.10
Scan devices, Please Wait...
Press <Tab> Key into User Window!
Hardware Initiate Failed, Please Check Device!!!
The BIOS does not be installed. Press <g> to continue!'
I also delved around the internet, and found that it is quite common for SATA hard drives to not show up in the BIOS or to show up as SCSI devices. In fact my new drive, like the old one, doesn't show up in BIOS, but does show up with its 'STM' reference number when starting up (before the boot from CD screen).
I found that, among other things, the 'STOP 0x0000008E' error can involve problems with other hardware, and so this might never have been a hard drive problem - that doesn't matter, as I've got a shiny new HDD now!
But might this be a problem with my RAM dying somehow? I've got two 512MB DDR400 PC3200 sticks. I have tried using each stick in each slot, but with no luck. So is it usual for ALL the RAM to get corrupted if something goes wrong? I read on another site that if the memory fails, it can completely ruin the hard drive.
I think that's it so far, and I'm running out of ideas. I'm not sure if I need to change anything in the BIOS settings - I think I posted them earlier in this thread. Maybe I need to just buy some new RAM(?)
I don't think it's a PSU problem, as on the alternate times that the computer starts up ok, I can see the presence of everything incl. the HDD, and can get through to Windows Setup all the way to the XP setup - I guess I'm supposed to press <Enter> rather than <R> for Recovery Console?
Anyway, lots of info to digest here. Heeeeelp!