Hmm... I did some brief Scroogle searches and got two hits that might be of interest:
(1): How to share an EXT2 partition with Linux
http://wiki.netbsd.se/How_to_share_a...ion_with_Linux
It says you should avoid the dir_index and large_file attributes, so be careful with using that e2fsck.
(2): How to mount FFS partition under Linux
http://wiki.netbsd.se/How_to_mount_F...on_under_Linux
Write support seems to be rather precarious, so let's be careful out there.