What kinds of partitions can be resized in Mac OS X v10.5 Leopard?
Mac OS X v10.5 Leopard can resize any disk partition except a Master Boot Record Partition. You can use Disk Utility to see if a partition is a Master Boot Record Partition, and also to resize eligible partitions.
Important: Resizing a Master Boot Record partition will erase all data on it, so be sure to back up important files on affected partitions first.
What is a Master Boot Record?
A Master Boot Record, or MBR, is the first sector of a partitioned disk volume. It contains information about how how your disk is partitioned. See this article for some advanced details.
Here are some third-party websites with more information: