Heh, Nevermind I answered my own question. For those of you that need to know...
----------
PS 2 consoles with version 4 boards may NOT be able to boot PSX backups using the traditional method. To play PSX backups on a v4 PS2, boot normally, but once you reach the startup screen ("Please Insert A Playstation CD"), press the RESET button once. The backup should now work.
----------
This method worked for me.
