external hd mac ntfs 3g could not mount
Install NTFS-3g in here: http://www.macupdate.com/app/mac/24481/ntfs-3g

Then install OSXFUSE: http://osxfuse.github.com/

MacFuse has been abandoned for a while now. Someone picked it up and rename it to OSXFUSE

If you want to use it for Mac and Linux, use FAT. If you want to use it for time machine, use HFS Journaled.