Josh, I've run your script once again and here's the SQL error I get:
[]Unable to do_query: ALTER TABLE w3t_Users CHANGE U_BirthDay U_BirthDayOLD INT( 2 ) UNSIGNED DEFAULT NULL - Duplicate column name 'U_BirthDayOLD' [/]
and
[]Unable to do_query: ALTER TABLE w3t_Users ADD U_Birthday VARCHAR(10) NOT NULL DEFAULT '0', ADD U_ShowBday INT(1) NOT NULL DEFAULT '0', ADD U_TimeFormat VARCHAR(6), ADD U_Ignored TEXT, ADD U_OC_Userid VARCHAR(64), ADD INDEX birthday_ndx (U_Birthday,U_ShowBday) - Duplicate column name 'U_Birthday'[/]
I think it shouldn't be hard to convert the three birthday fields into one using some query, but not for me

U_BirthMonth , U_BirthDayOLD and U_BirthYear should be combined into the new U_BirthDay format...
Thanks in advance!
Pasquale