CTRL-T opens a new tab in Navigator.
Check out Mozilla 1.7 at mozilla.org on the web. Their site has lots of instructional material that also applies to Netscape.
Personally, I found Mozilla 1.7 to be a bit better than Netscape 7.1, especially in printing pages. Definitely worth the large download.
I've not tried firefox as it is still in beta (not for me).