Got an IDE hard drive from an old Linux box and you want to access its contents with your Mac, without setting up a temporary Linux system and networking it? Get a Firewire enclosure and download the Ext2 filesystem utility for Mac OS X. Ext3 is also supported, though journaling is not.
Sadly, the ReadMe says Mac OS X 10.4.x (Tiger) is not yet supported, and sure enough, I couldn't get it to work.