sorry to have led you up the garden path.
having looked at this properly, i realised that the server behaviors i mentioned do not actually update the orderid, it is an auto increment.
there is a way to get a mysql database to start the autoincrement of an integer field other than 1.
here it is...
in phpmyadmin, click on the sql tab and type in the following...
(assuming your orders table is tblorders and you want the autoincrement to start at 101)
ALTER TABLE tblorders AUTO_INCREMENT = 101;
i think that shouled be all you need.
if this doesn't work, let me know, and i will try to find a more solution for you over the weekend.