Missing or corrupt c:\windows\system32\drivers\ntfs.sys

A copy should work as long as it is the same media type i.e. full or upgrade version, edition i.e. Home, Pro etc. and revision i.e SP as the original install.

Should I mention drive imaging here or not?

There are lots of things you COULD do but it would depend on the current state of corruption on your existing install which is difficult to ascertain from a remote location.

They are going to send the disk that was applicable at the time - it is an old PC - and then walkthrough the repair - although I do know how to do that part.

Although the error message seems uncommonly specific for Microsoft, consider the possibility that it is not pointing directly to the cause of the problem. One possibility is that the driver is intact but is not loading for some reason. While waiting for the install CD to show up, try running a system memory check using memtest86 http://www.memtest.org/ . Memtest boots from linux, so will work even if you can't get into Windows XP. A bad segment of memory might be addressed at exactly the same point in loading windows at bootup, and cause the failure of the specific driver to load--interpreted by the OS as a missing or corrupt driver.
 
You might also try to find the hard drive manufacturer's test utility. Most drive makers have a downloadable test program version that will boot under its own linux or dos operating system like memtest.  A bad hard drive sector (and consequently corrupted ntfs.sys) is a more likely cause than memory failure. If you can't get a boot after trying to restore the driver, then a check of the memory, and running chkdsk from a command line in the recovery console after booting from the install CD may help. If not, then a repair installation of Windows XP would be the next step.
 
http://support.microsoft.com/kb/822800
http://support.microsoft.com/kb/555531
 
http://support.microsoft.com/kb/307654
 
http://pcsupport.about.com/od/operatingsystems/ss/instxprepair1.htm
 
http://support.microsoft.com/kb/917964
 
 
 
 

And the follow up.........I got the disk and they tried to fix it but the OS has gone to a better place. Re-install the only option.

Cheers OM. I'm just testing one more thing and then bringing in some help. I've a had run of PC issues recently with HDs. The only common denominator is me.! I reckon I can break anything but always without touching it. Keyboards, speakers, monitors.... the list is endless recently. One minute they're ok and the next..... whoosh...... it's toast. I'll be out busking to pay for all this. I'm not selling another kidney. It's a pain to meet, drug and operate on people without their consent.