Correct, at this time Netscape hasn't been certified. We currently support IE6 and Firefox 1.0+. Once reason we've lowered the priority on Netscape certification is that recent reports say the Netscape usage is less than 1%.
http://www.e-janco.com/browser.htm
I just checked the webstats for zimbra.com so far for the month of September...
Netscape 0.39%
So even less that the report I sited above. Nonetheless we'd like to be compatible with all major/popular browsers. Since this is open source we welcome you passionate NSCP uses to try it out and submit patches.