I downloaded source code from zimbra website, and tried Ajax examples, found it isn't work, at least some css files are missing.

where are those files?

@import url(../common/img/hiRes/dwtimgs.css);
@import url(img/hiRes/imgs.css);

Could you release REAL source code? http://www.zimbra.com/forums/images/icons/icon10.gif
Talking