Download and install and RUN the boothack ipk. This will handle all the script issues for you: http://www.pointlisse.com/PMA430/File/boothack_pma400_0.2.zip
Once it has been applied, shut down. Connect to USB and rename the /System/aimage.img and replace it with the openPMA aimage: http://www.openpma.org/openPMA_0.1.1_20060917.zip
Disconnect from USB and try to boot. If you see openPMA run, you're good-to-go. If you get an error message, connect to USB, and restore the Archos firmware and try the boothack again.