Right, having got rid of all of the cards apart from the graphics card (this mobo has no VGA out) I attempted a new install of 98, which failed with the same fault as before - machine gets to the splash screen and then fails.
However, when I got rid of my Gig of RAM, leaving only 256 MB, the machine started in safe mode. I am guessing that win 98 was overwhelmed by the available resources (or possibly a faulty RAM strip.) . I have looked in the device manager and found no conflicts.
Is there anything else I ought to look at while I have the machine in safe mode?
My next inclination is to try for a restart.