Alright!

I've found the answer for myself - with thanks to
jmiller47 on
(as usual, discovered using Google)
Go to the "Printers" folder, drop-down menu:
File > Server Properties > Drivers tab.
From here you can Add, Delete, Update or check Properties of any printer drivers.
Simple yet obscure - even the online "Microsoft Windows 2000 Server Documentation" > "To install new or updated printer drivers" gives only the same explanation as Jim did above.
However, warnings from my past few hours experience:
I have found it better to use the usual
Sharing tab >
Additional Drivers route for adding or re-installing drivers, otherwise they don't get "checked" in the printer's "Additional Drivers" list.
Also, you must use the standard
Advanced tab >
Update Driver route for updating the Windows 2000 driver (otherwise "file is in use" errors) - but this creates a "... (Copy 2)" of the original printer object, using the updated drivers, then deletes the original, losing the original preference settings (including previously installed "Additional Drivers"

in the process. So you get to practice the routine again...
And messages requesting the Windows 2000 CD for .inf files seem to be a dummy - as long as I browsed to an acceptable driver elsewhere, it was happy (but it never learns to look for itself - no better than Windows 9x).
Hope this helps somebody else out there,
Alistair