think it depends on which php you're running, or more importantly, if you have apache set to parse php3 files or not. I think the difference is that instead of being .php files, the php3 one uses .php3 files.
So if your apache doesnt parse .php3 files, then I'd get the .php one (which i think means if you're on php 3, then get the php 3 pne, otherwise just get php)