A few more points:
1. Some posts on a Debian support forum suggested adding a Modeline parameter to the Monitor section as my monitor is wide-screen, hence not standard. I added this using an online generator, but did not work.
2. The command xvidtune was suggested to get the modeline. This command returned an error message - "video modes cannot be tuned for this chip". I can't remember the exact message as I am not at home, so can't check it again.
3. Is this because I'm using vesa driver? Using the ati driver causes the X to stop starting and it asks me to fix the xorg.conf file. The error is (approximate again) - "No screens found".
Regards