two things you can do:

Use one of these two as the div containing your skin:

<div class="<%=IIf(Request.IsAuthenticated, "Authenticated", "Unauthenticated")%>">

OR

<div class="<%=IIf(UserController.GetCurrentUserInfo().Username.tolower = "admin", "AdminLoggedIn", "NotLoggedIn")%>">

Now use the injected CSS class to make the panes wider if a user is logged in.

The first one will check if anybody logged in, the second if the admin logged in (or any other user you want).

HTH