The engine can be rebuild against MySQL 4.1 but you'll need a number of things. I've done that quite some time ago, follwoing the description on www.4ovms.dyndns.org - but the data seems to be lost there
. Jean-Francois Pieronne (who's doing the MySQL ports) has it in his MySAL forum as well but I cannot refind the site 
BTW: On the last bootcamp I requested an update of the PHP engine, it will come - some day....