Search for the universal login mod will help you.
Once you have that sorted a simple bit of code at the top of the page after including config.asp and inc_header will sort out who should be there and who shouldnt, in this example anyone who's not an admin and attempting to view the page will be redirected to default.asp, you could display a message or something instead, if you replaced <> 4 with = 0 or < 1 then it would stop non-members viewing, with < 3 then only moderators and admins would be able to view it.
<!--#INCLUDE VIRTUAL="forum/config.asp" -->
<!--#INCLUDE VIRTUAL="forum/inc_header.asp" -->
<% If (mLev <> 4) then
Response.Redirect("default.asp")
end if %>