More visual styles can be downloaded from third-party sites such as www.themexp.org but you need third party software to run them. One such
software is StyleXP, which again can be downloaded from www.tgtsoft.com
The only Microsoft certfied way to add additional themes that change your
Windows GUI is with a program called WindowBlinds (www.windowblinds.net).
Other methods to add visual styles involve patching uxtheme.dll to disable
Microsoft's digital signing protection (either in memory or physically on
the disk).
I don't know about Netscape modern but you can download a Mozilla visual
style here for WindowBlinds: