How to create Sub Sub domain Multi User blogs?

Hi to all I would like to create a big WordPress network with this structure:

• sitename.com (Main website)

  • cat1.sitename.com (sub website)

    • cat11.cat1.sitename.com (sub-sub website)
    • cat12.cat2.sitename.com (sub-sub website)

  • cat2.sitename.com (sub website)

    • cat21.cat1.sitename.com (sub-sub website)
    • cat22.cat2.sitename.com (sub-sub website)

  • cat3.sitename.com (sub website)

    • cat31.cat1.sitename.com (sub-sub website)
    • cat32.cat2.sitename.com (sub-sub website)

Is it possible using only one wordpress installation with subdomains? If it is not is it possible to share userdatabase (and why not also posts and all the stuff) between all the websites?
Is there anyone that already did it and can help me to achieve this? Thank you very much!

While this question is several months old and you’ve probably figured something out already, I figured it was worth answering anyway. This is possible to do using the WP Multi Network Plugin. WordPress has the underlying structure to accomplish this, but no accompanying UI — this plugin merely offers that interface.

Some things are not completely shared across Networks, and I believe Users are one such example. If I remember right, users can span multiple networks, but it needs to be done by a super admin. Anyway, play around with it, you’ll get it working how you want!

Cheers~