it sounds like it's just the seals. Is this automatic, or manual? Since you say moonroof, I assume it's the automatic one.
you would only need to replace the glass if it were cracked and that was what was letting water in. It's definitely your seal, you should either buy a repair/replacement kit from nissan, or bring it in to have a nissan tech look at it. <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt='
'> I know how you feel though, my windshield leaks on the top right corner, and when it rains, I have drops of water falling on my left hand/arm. It's annoying, but doesn't sound quite as bad as your moonroof!
Good luck!