I have a requirement to build one parent site and few child sites..using domain and sub-domain concept and want to have installations of joomla at parent and all sub-domains. But I want only my parent site to hold user data and Alpha user points data while my child sites would be hosting components and modules separately and use user data and Alpha user points data from parent site.

Could any one suggest me is it a good Architecture to go and is there any extension or component already available to achieve it. Example
below:

parent site movies.com Child sites braveheart.movies.com, troy.movies.com

I will have forums, blogs and other component installations at braveheart and troy sub-domains seperately while my Alpha user points and users db/tables would reside at movies.com(main domain).

It's like single-sign on or Centralised Alhpa user points, but free to install same component and modules at different sub-domains.

Highly appreciate any replies or solutions proposed

someone help me findout.........