Thanks Al
The plot has thickened since then and I'm sadly not far off being back to 
square 1.
All was working fine until I noticed I'd lost my wheel mouse.   That and the 
screen was marginally too big for the monitor.   I did try displayconfig-gtk 
(couldn't find DisplayConfig in Synpatic) - was this the one you meant?
However, the stage I'm now at is being unable to get any sort of graphical 
display at all - not even the username and password screen.   So much so in 
fact that the only way I can currently get in at all is either ssh or 
Ctrl+Alt+F1 to get me into some terminal mode.
However, in trying to run dpkg-reconfigure xserver-xorg, I'm getting an 
error because the server's still running.
According to 
http://ubuntuforums.org/showthread.php?t=83973
I can do gdm stop to do this - but that's not working either i.e. somehow 
it's not stopping the server so I'm guessing dpkg-reconfigure with the 
server still running is a non-starter.
What I need to do is boot, stop X from starting, dpkg-reconfigure to get the 
correct settings, and gdm start (repeat until settings are correct) but as I 
can't start X (or even login!) I'm a bit sunk.
Ctrl+Alt+Backspace does kill the X session but doesn't give me a prompt 
after its messages.
Something's gone wrong and I can't see where the answer lies.   I'm happy to 
upgrade to gutsy but unless a clean install, I'll need to transfer quite a 
few files first so I'm keen to stick with feisty if poss.
Sorry this email is a bit disjointed - but everything I've tried to fix this 
has failed!
Cheers
Rob