Actual calltip support (shown when typing function arguments) for more languages is on the TODO list, but is not a high priority at the moment (ideally someone familiar with each language and C would extend the current parsers).
Is there not any library that can be build upon? For instance for syntax highlighting in webpages there is geshi.
Maybe there's something similar for these tag files.
I still don't know how other python IDEs succeed in providing this kind of autocompletion for any module that one imports.