I agree about P5NCI, would be nice to see more on this. There's also a similar looking thing called FFI on CPAN. I wonder how these compare/contrast?

Sadly, I couldn't get these to install on Windows XP, (a while back so I can't remember what problems were holding me up) but there is Win32::API. Also the Inline and InlineX modules are great of course.

Of course there's Extending and Embedding Perl which covers XS, a bit of Inline::C and PDL, and embedding Perl in C. But things have moved on a little.