Not a great deal, really. Administrators have more abilities on the boards and have pretty much full access to almost every part of the software. Moderators have less and it can vary from site to site. Mods can close/edit/delete threads/posts and ban people. Admins can do all that plus more - name changes, personal information changes, hard-deletion of things that mods might only be able to remove from general viewing. Most of the options we have are the same as the mods.
As Steve is the owner of this site he has unfettered access to all of the software. Dark Drakan and I can't do everything he can but we still have a few more options than Angelo Credo and Tony Redgrave.