Problems with ImageCreateTrueColor

Hi, I'm running a Matrix server with a modified RedHat Linux install. I've installed PHP 4.3.0, and GD 2.0.10, but the ImageCreateTrueColor and ImageCopyResampled functions are not available, trying to use them just causes browsers to stall, the document returns no data and no errors are left in the server logs. I've tried running NM on the GD libraries, and both functions are there, I've tried reinstalling PHP 4.3.0 to use the supplied GD, AND compiling with my external libraries, but I'm still getting the same problems. I really need those two functions to provide decent Image Upload services on the server, because 256 colours with ImageCreate/ImageCopyResized is just not good enough for my clients. Can someone PLEASE help. I've tried #php on IRC and no-one seems to have a clue what the problem is. My eternal gratitude in advance to anyone with any suggestions Kieran