Greetings - In the end, disabled the option ROM in BIOS setup which opened up 64k window which it seems to need to be able to get a page frame.
Still not sure why the same system, same BIOS settings (before above change), was fine under XP Pro and not MCE... That was the bit I was most curious about, as in my case it clearly wasn't a mo-board or hardware issue -just a different XP version issue.
Did try setting EMM=RAM in config.nt and have nothing in autoexec.nt and still had problem before disabling option ROM.
Have deleted the EMM=RAM line now and all's well.
Thanks for the replies and hope the above helps someone else.
~j