I'd write out the logic in pseudocode (or function names) beforehand, just to make it easier to figure out the logical flow:

display_login_form()  unless logged_in();
display_admin_view()  if     is_admin();
display_normal_view();

sub logged_in
{
    # check for a cookie
    # check for a 'pass' parameter if there's no cookie
    # create a cookie if there's a 'pass' parameter but no 
    #    cookie already
    # return true if either one is valid
}

sub display_login_form
{
    # print a form that asks for the 'pass' parameter
    # exit;
}

sub is_admin
{
    # check if the given password matches the admin password
}

sub display_admin_view
{
    # show the administrative view
}

sub display_normal_view
{
    # show the normal view
}
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I switched to curly braces on the new line after working with Ovid. They take up a bit more space on the screen, but that's a good impetus to keep my subroutines short.