Yes, it can be done, for those who want to know, and this is the resultant boot.ini file...
[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /noexecute=optin /fastdetect
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professionnel" /noexecute=optin /fastdetect
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons
The US English version is on drive C: (Partition 1) and the French version is on Logical drive D: (Partition 2)
They are currently directly sharing a Documents folder, (The Shared Folder system has been removed) Email folder and Music folder on drive E: (Partition 3) and, as soon as I have fully installed and tuned the French version they will be imaged to drive F: (Partition 4).
I should be totally bald by then...