Well, it took a bit of doing - but we're there!! Yay!!
Turned out that the drive assignment was because I had installed an internal card reader into USB controller 2 - and it was read as four removable media slots. C D E & F
This apparently pushed the HDD to be named drive I behind the four card slots and two optical drives. G & H.
Removed the USB plug, re-installed XP, reconnected USB. Then set about doing all the updates again.
Off to the shop for an extra digital video cable, then she can have the new graphics card installed.
Made the machine connect to the home network, found it's printer (but, curiously, not the network printer) - just need to load Office, update Office, transfer the .pst files for wifeys e-mail and then install her old IDE drive as a .pst back up drive.
Also have to figure out how to control RealVnc to see the machine from my desktop viewer. The server has been installed already.
Phew. I need a beer.
Many thanks for all your input everybody. Very much appreciated.