Q per adding text to png

Hello, I know how to create an image via php but what if I have an image in the root called 'button.png' and I simply want to add text to it so button.png has the text I specify? When I *create* images, I can add text just fine. But to overwrite the blank image to have text? Do I have to have that freetype installed? I can't use those font commends on win 98 and when I install php 4+ on linux, I won't know how to call those font commands can I just use the same querystring method $string = urlencode("where"); so ?where=Test would allow 'test' to be in button.png? or is this not allowed in php? Thanks