Creating 4 website with same database and admin panel

Hi everybody,
Thanks for being such a lovely community.
I am planning to develop around 4 product catalogue websites. The functionality of all the websites would be same. however the design, images and css would be different.
All the 4 websites will use the same admin panel, forums and database(MS Access) also.
How should I create such a system.
I dont understand what kind of folder structure should I create.
Ideally I would like to create following kind of folder structure.
(Root Folder)Admin Website  ----> Website 1 (subfolder)

                                              ----> Website 2 (subfolder)
                                  &n ...