sadly CPAN has no way of specifying such dependencies

What you can do is reflect the C library with a Perl distribution (e.g. Alien-wxWidgets). During installation, the distro checks if the necessary C library is installed. If not, the distro either fails to install itself or it installs the C library.

I think in windows the perl distributions come with their own packaging systems

I don't think there's anything Windows-specific about PPM. It's just that there are only repositories for ActivePerl builds. (I think they usually also work with Strawberry, and I think a change to 5.12 makes is so they always work.)

but then you have a much more limited set of up-to-date modules

There's an amazing list of up to date modules. Someone's probably running an automated tool. But it's probably not the same story for modules with external dependencies such as XML::LibXML.

I am not sure how well they handle external dependencies.

They incorporate external dependencies. XML::LibXML is now available from AS's repo for 5.12: 

>ppm install XML::LibXML
Downloading ActiveState Package Repository packlist...done
Updating ActiveState Package Repository database...done
Downloading XML-LibXML-1.70...done
Downloading XML-SAX-0.96...done
Downloading XML-NamespaceSupport-1.11...done
Unpacking XML-LibXML-1.70...done
Unpacking XML-SAX-0.96...done
Unpacking XML-NamespaceSupport-1.11...done
Generating HTML for XML-LibXML-1.70...done
Generating HTML for XML-SAX-0.96...done
Generating HTML for XML-NamespaceSupport-1.11...done
Updating files in site area...done
 110 files installed

[download]

In reply to Re^2: ERROR in XML::LibXML installation by ikegami
in thread ERROR in XML::LibXML installation by satzbu

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