FP2K & hover buttons not working

We use FP's hover button feature which seems to show up on some web browsers and not others. What is the key factor that needs to be installed in a browser for this work? I know many FP extras only work on Internet Explorer (hey, it's a Microsoft thing!) but I have had complaints from web visitors using IE 5.5 and not seeing our hover buttons. I thought the key was having Microsoft Virtual Machine installed as part of the IE install but someone who has VM installed still can't see it. Netscape appears to need Java Plug-ins but I'm not sure what. Microsoft's knowledge base does not really address this problem anywhere. Point blank, what are the minimum requirements of both Netscape and Internet Explorer to be able to view these hover buttons? Thanx!