You can boot from the Vista disc and repair the MBR which rebuilds it with Vista as the single boot option.
With the MBR fixed, you can boot Vista and use EasyBCD to add XP again.
The first time I rebooted from the Vista disc, I'm pretty sure that the repair panel was empty.
However, on the second attempt it did list the Vista installation.
After trying
most all of the "bootrec /fixmbr, /rebuildboot, /scanos options, the last one I tried (which also happened to be the second on the list in the windows help section) was the "bootrec /fixboot" option, this was successful except the PC then only booted into Vista, with no sign of XP. (as you point out above)
Well, me being me, "in for a penny, in for a pound" I tried the EasyBCD option and after adding XP into the "Add/Remove Entries" option the system is now back up and working as it should be.
But I have to admit most of this was just trial and error, but it worked.
Many thanks for your input, as it also confirms that what I did was correct, just went the looong way round to get there (as usual).
"Now to backup (Ghost) the C: drive so as not to lose the MBR file again".