So now it gets more complicated!
1. If I try and boot normally with the SATA drive plugged into the original Adaptec raid card, I get a heap of 'disk i/o error status = bla bla' messages then the famous ntfs.sys is missing.
2. If I connect the drive to the motherboard SATA connector, I get the 1st W2K splash screen then a blue error screen 'if this is the 1st time you've seen this message bla bla'
So at least the drive is trying, BUT
3. If I boot from the recovery CD, F6, load the SATA driver (found inspite of DELLs best endeavours!), press R, it goes finds and inspects the SATA disk but then comes back and tells me 'either this isn't server 2000, or there isn't an operating system on the disk'.
4. If I slave the drive in another PC I can see the system partition with a winnt folder and in the right place a ntfs.sys file (which I've replaced and tried again incase it was corrupt (see 1 above).
My forming conclusion is that because of the disk i/o errors reported in 1 above, I've got a drive that is dieing.
So back to my original quest - how can I rebuild the MBR on a SATA disk? I'm running out of options.
Any ideas appreciated, and thanks