What ever you do as administrator should affect all profiles - i.e. all users. Some Windows settings, such as the Regional Settings, have the option to affect all profiles or not.
It's better to use an account with administrator rights than it is to use the administrator account. Right-click "My Computer" and choose "Manage". Look for "Users and Groups" in the left-hand pane. Click the + to expand the option and click on the "Groups" folder. On the right, double-click on "Administrators". Add your username to the group. Paul talks about adding the username to the "Power Users" group. This is like being administrator, only with fewer rights/permissions. I would avoid this purely because you may encounter problems with some programs and installing some programs. Upto you though
In addition to the usual profiles, you also have:
All users - anything in this profile affects all users. So if you put an icon in this profile's "Desktop" folder, the icon will appear on the desktops of all users.
Default user - this is a sort of template profile used when new profiles are created.