Sorry Dave, everything I have seen so far seems to follow my theory that the MBR is now missing from your system as it would have been stored on the failed ME drive
So the method above should do it but would take a similar time to the original installation and would require reactivation and I think the windows updates again.
This second option may work and should be quicker
How to access the Recovery Console:
The Recovery Console can be run from a Command Prompt by going to Start->Run and enter "CMD" to open a command window. Type HELP for a list of functions.
To run the Recovery Console from CD boot with the Windows XP CD (or with the optional 6 floppy disk set) and select "R" at the Welcome Screen.
The screen will switch to black and you will be asked which installation to log on to. If you only have one installation you will press "1". Remember that numlock is off at this time.
Next you'll be prompted to enter your Admin password. By default it is created blank so just press Enter.
At the C:\Windows command prompt type "Help" for a list of commands you can use.
How to Repair the Boot Sector:
If XP won't start it may be due to a damaged boot sector or a missing or corrupt ntldr or ntdetect.com files.
To replace damaged ntldr and ntdetect.com you can copy fresh files from the XP CD using the COPY command. Boot with the XP CD and enter the Recovery Console (as above). At the Command Prompt type the following (where "X" is your CD-Rom drive letter) allowing the files to overwrite the old files
COPY X:\i386\NTLDR C:
COPY X:\i386\NTDETECT.COM C:
To repair a damaged Boot Sector at the command prompt type FIXBOOT and press Enter. Then answer "Y"
I would suggest trying the FIXBOOT option first Dave, that may be all it needs.
Hopefully someone else will confirm this or not before you get chance to try it