You can do what you want, fairly simply, with XML::Writer. The result can be read back with XML::Parser.

First you have to decide what kind of XML you're going to write. That means settling on a DOCTYPE declaration or a schema of some kind. What are XML tags and what are data in your hash?

Once you have a doctype to settle that, the rest is easy. Note that since hash keys are unordered, they should be represented by XML that is also independent of order. Where order matters, arrays are used.

I recommend Perl & XML by Ray & McIntosh (O'Reilly, 2002) to get you started. Whatever you do, make absolutely sure that what you write is truly compliant XML and not some creole of it.