In order to run Digital Performer on your Intel based Mac computer you'll need to have version 5.1 or later. MOTU does not officially support earlier versions of DP on Intel based Macs. The link below is to the MOTU website with their official statement. This will result in the Gearbox Plug-In not functioning properly within the recording application.

http://www.motu.com/techsupport/technotes/intel-mac-compatibility/view?searchterm=Digital%20Performer%20Intel%20Macs