How to send gzip content

Hi, this question is not about compressing HTML content, but SVG or VRML! i want to compress the entire output with gzip before sending it to the client. I found the function ob_start('ob_gzhandler') but this seems to compress only in special cases. (Actually I don't see if the content is compressed, how can I check this out?) But for my SVG or VRML content the plugins always support compressed files, even if the browser doesn't. Therefore I want to ensure sending compressed content. Then I found the "gzencode -- Create a gzip compressed string" function. I tried to use it like this: <?php ob_start(); ?> SVG or VRML content <?php $sContent = ob_get_contents(); ob_end_clean(); echo gzencode($sContent); ?> But now I get this error: Fatal error: Call to undefined function: gzencode() ... What do I need to do to use the Zlib Compression Functions? System: PHP Version 4.2.2 Windows NT 5.0 build 2195 Apache/1.3.24 HTTP_ACCEPT_ENCODING: gzip, deflate