Apple has updated GarageBand '08 to v4.1. This update addresses isolated graphic display issues, compatibility with 3rd party audio software, fixes minor problems with Magic GarageBand, and supports general compatibility issues.
Note: In order to install this update you will need to download the iLife Support 8.1 update first. The iLife update supports system software components used by all iLife application, improves overall stability, addresses a number of other minor issues and supports general compatibility issues.