I use a MacBook (C2D, 2.16 GHz, 160 GB HDD) which multiboots OS X and four Linux OSes.
I can easily access/read/write OS X files from all of the Linux partitions but the opposite transaction is less straightforward.
I came across Ext2fsx
and installed it in OS X.
However, it seems just a little temperamental. For example, of the eight (/ and /home for each of the four OSes) ext3 partitions I have on my MacBook (Ext2fsx is claimed to cater for ext2 AND ext3 partitions) only two actually are mountable. I have made many different attempts to mount the remaining six, even after unmounting the two mountable partitions, but all to no avail. I can, however, read almost all of the files on the mountable partitions although writing is not possible.
Additionally, I have an external usb HDD which has twelve ext3 partitions. When I plug this into the Mac, only eight of the twelve ext3 partitions automount.
Although ext2fsx seems to me to be a potentially extremely useful little utility, there is really very little general information available on the web.
I would very much like to hear from anybody who has some practical experience with ext2fsx, good or bad, and who can perhaps help me make some progress in understanding how to get more out of it.