Chetan and all,
Actually these project doesn't need any formal joining.
1) You can download the code from the SVN repository
2) You can read the email archives of the devel mailing lists
3) You can read the blogs to see the current status of the project
4) You can play with the code and read the google code project wiki to know what has been done till now
5) you can run the project and check what are the issues and what more can be done
6) You can write mails to the devel mailing list groups with your ideas and even send patches for some issues
7) your participation in the discussion groups will automatically mean that you have joined the project
8) As soon as you start contributing more you will eventually be considered a developer and will get committer status
I hope this explains the way you can join the projects. This holds good for any open source project out there.