Joy of Think

Android use YAFFS2 as its root filesystem.
For extract it, you can use a tool named "unyaffs", which can be found in http://code.google.com/p/unyaffs/.
This tool will extract content of image file into current directory. You'd better to create a new directory to hold them.
For making YAFFS2 image, please use binary tool mkyaffs2image. The tool is built in ./out/host/linux-x86/bin/mkyaffs2image