To get Ext3 and Ext2 support in OS X, just download the Fuse-ext2 driver from this Sourceforge page and install the package. When you reboot, you should have read access to your Linux drive.
While the drive does support reading and writing, it’s set as read-only by default. You can enable it by tweaking a configuration file, but I will note that while many have had success with this method in Snow Leopard, it keeps throwing me an error when I try to write to the drive, so your mileage may vary. To make OS X mount the drive as read/write, just navigate to
/System/Library/Filesystems/. Right-click on the
fuse-ext2.fs file and hit “Show Package Contents.” Then, drag
fuse-ext2.util to the desktop, right-click on it, and hit “Open With”, choosing TextEdit when prompted.
Use Cmd+F to find the line that says
OPTIONS="auto_xattr,defer_permissions" near the middle of the file. Add ,
rw+ to that line inside the quotes, so it reads:
When you reboot, the drive should be mounted as read/write. Note once again that write support is a bit buggy in this driver, so just be wary.