i haven't used the following code in a forum environment but i have used it elsewhere and i imagine the code could be improved upon.
I put it in the global.asa file which would reside in your web root directory. on session start the global.asa should fire up and execute the code.
Sub Session_OnStart
' Make sure that new users start on the correct page of default.asp...Can't jump into middle of site
startPage = "default.asp"
currentPage = Request.ServerVariables("SCRIPT_NAME")
' Do a case insensitive compare, and if they don't match, send the user to the start page.
If strcomp(currentPage,startPage,1) Then Response.Redirect("http://www.mywebsite.com/" & startPage)
End If
END SUB