I have noticed that if you have the php setting for zlib.output_compression set to 'On' AND you attempt to use hte ob_gzhandler handler to ob_start () the output you get in the browser WILL be garbled in PHP 4.2.3. I'm guessing that the output buffering is compressing the output to be sent, and then zlib is doing it a second time, but the browser is only uncompressing it once.
But using either one will give you the same results (compressed output from the script)