Zlib sources doesn't include this package, because that damn thing didn't 
fit in attachment size limit. Zlib sources what this plugin uses is the same 
as the one what comes with NSIS zip2exe sources and it's slightly modified 
zlib 1.2.3 so you better use that one.

But you can download the right Zlib sources here:
http://forums.winamp.com/showthread.php?postid=1825648#post1825648

Or you can use the one what comes with NSIS zip2exe sources.