"Inline::C is a module that allows you to write Perl subroutines in C". There a whole cookbook available with plenty of examples, everything from a 'hello world' to calling up Windows Messages boxes. The C module is generated, compiled and cached, the first time it is invoked. If you modify the C code, it rebuilds the cached module automagically.

You can pick it up from CPAN (including cookbook). The whole thing even works on Windoze, (though if you're using ActiveState's perl, you'll need to have Visual Studio).

Enjoy...