He estado echando un vistazo a las url's que me has pasado y a las librerías js y creo que ya se por qué no funciona el menú en NS:
El autor del js coolframe.js (www.bratta.com) no está revisado para funcionar con la mayoría de las versiones de NS. Básicamente solo funciona en 3, en las versiones 4.03, 4.04 y 4.08.
Esto quiere decir que su potencial es bajo ya que estas versiones son bastante antiguas. Deberías bajarte la última versión de este menú y así poder aprovechar realmente su potencia para los dos navegadores mayoritarios.
Si no fuera posible porque no hubiese una versión más reciente, pues lo tienes un poco mal ya que, las modificaciones las deberías hacer tu a mano.
Siento no haberte podido ayudar más pero no está la solución en mis manos sino en las del autor original.
Si deseas alguna alclaración más, ya sabes cual es mi nick.
Manz
PD: Te adjunto los comentarios del autor del coolframe.js.
/*******************************************************************************
Copyright (c) 1999 Thomas Brattli (www.bratta.com)
EXperience DHTML coolFrameMenus - Get it at www.bratta.com
Version Beta 1.0
This script can be used freely as long as all copyright messages are
intact.
Visit www.bratta.com/dhtml/scripts.asp for the latest version of the script.
(You can delete the comments below to save space)
Known bugs:
Opera 4: This menu is very close to working on Opera, but as far as I could
figure out opera don't support innerHTML or document. CreateElement() which
makes the changing of the text inside the submenus hard to do. If anyone
know a solution to this please let me know.
Netscape 6: This will not work on any Mozilla version below M17 (no innerHTML support)
Netscape PR1 is M14 I think. It should work on Mozilla, but I seems to be having
some problems with reaching elements over frames. I think that this is a bug
in Mozilla and hopefully they will fix the framesupport sometime soon.
Explorer 4 for mac:
It will not work in this browser, nothing does. It works just fine in Explorer 5
for mac though.
Script checked with:
PC
Netscape 4.08
Netscape 4.03
Netscape 4.04
Internet Explorer 4.01
Internet Explorer 5.0
Internet Explorer 5.5
Mozilla M17 <-- Not working yet
Opera 4 <-- Not working yet
MAC
Netscape 4
Explorer 5
Last note:
I would reccomend to not use to many items on each menu. You will get
flickering on older machines if you do... Try keeping it at a max of 10
THE REALLY LAST NOTE:
If you have this linked js file inside another directory then your menu.html
file be aware of that Explorer treats realtive links relative to menu.html while
Netscape treats it relative to this file. So I suggest that you keep this
file and your menu.html in the same directory.
If there are features you think should be added to this menu please
post it in the coolMenu and coolframeMenu forum at my site:
http://www.bratta.com/dhtml/scripts.asp?url=forum*******************************************************************************/