Ok, I also got a blank page on NS 4.7. I took a look at your source and I think I see what's the problem. I think Netscape is barfing on the code because you have a frameset with only 1 frame. There really is no need for this. Just make your main.htm your index page (and adjust all internal links accordingly).

Right now, NS users should be able to see the site fine by going directly to http://www.nest.dtn.ru/main.htm.

Hope this helps.