Sammy: I don't know if there is such tool, but converting html to XHTML isn't easy as far as I know, so automating the process of converting several files might be a difficult task. I think HTMLTidy (a free tool) does clean up most of the code but I have no idea of an automated tool to do that.
Edit: I just tried
this online free tool and although not beautiful, it does convert html to PDF. Still far from automating the process though. Might need to investigate a bit further to find something useful.