if anyones game to try live partition resizing in leopard's disk utility you could use this (i havent tried it yet). if it works you can resize partitions without reformatting. DO NOT do this with tiger's disk utility as it will reformat your disk.
the other option is ipartition
http://www.coriolis-systems.com/iPartition.php which can resize partitions with out reformatting like leopard's disk utility. note: you have to be booted into a different disk than the one you want to work on. so if you want to resize partitions on you main hard drive you have to make a boot disk (see coriolis homepage) or boot into a cloned system on an external hard drive or another hard drive.