If you are wondering whether the SuperDrive in your Mac is dual-layer capable, or whether it can store 8+ GB of data on a data DVD rather than 4+ GB, have a look at the System Profiler app (you can Spotlight it to easily find it if you use Leopard), and check Hardware, Disc Burning, DVD-Write. If you see the tell-tale DLs in the description, you're good to go. Just buy the appropriate media.
