Reuven,
I'm not sure I perfectly understand what you're after, but you can give any user "site-wide admin rights" by granting "admin" to that user on object 0 (zero). The UI for this is somewhat opaque, but I figure you'll find your way from the permissions/ page.
If you're talking about the file system, then both of you will want to belong to the "web" group.
HTH.
