[Zope] Slow calendar rendering in Netscape

Hi, I'm playing with the calendar tag, based on code from the Zopista at zopezen (on zope 2.3.2), and have found its really slow to render in Netscape (v 4.7), whereas IE5 zips through it. I've tried putting the dtml- method in a RAM cache (no change) - is it the brower struggling to render a complex table? Any tips from speed freak zope heads? Or should I not use a calendar with NS, and can I use HTTP_USER_AGENT to filter it out? Cheers, Rob