So you can't use some OSX software on older versions sure as your 10.3 version? Hmm... another reason to dislike the OS.
There were significant changes between 10.3 and 10.4 - Quartz Image processing (or something like that) which means 10.4 is generally the base OS X release that people write s/w for. Even Apple, the swines! I will get around to buying 10.4 or 10.5 retail eventually...