PNG and GD-lib trouble

I am running PHP 4 Release Candidate 2 with Apache 1.3.9 on a RedHat 6.1 box. I have started playing with the image functions: I have createde a small PHP script that takes a GIF file, crops it and outputs it directly to the browser (using the header()-function to tell the browser, that a GIF is coming up). Now, I'm not a GIF fan, so I would like to output it as a PNG. It doesn't work however. I get the following error: Warning: ImagePng: No PNG support in this PHP build in /www/htdocs/gp.php on line 9 phpinfo() tells me, that GD is support is enabled, and that my GD version is "between 1.3 and 1.6.1"! Furthermore it says that GIF support is enabled. I thought (have read on the net) that PNG support was built into newer PHP versions. Is this true, or do I have to obtain a newer version of GD lib and recompile to use imagepng()? And if I do, will I loose things like imagecreatefromgif()? Help me promoting PNG, people! Thanks, Lars