First of all, I don't believe you will be "penalized" for submitting duplicate press releases. The nature of press releases... even the purpose of press releases is to be available to the media in the places they use to find them.
As said earlier, there isn't a press release software. Every distributor has its own guidelines and templates for the way they prefer to publish press releases as well as guidelines for press release submission.
As far as tools for validation, it is up to the publisher to make sure the releases validate on their distribution sites. If you want to add your press releases to your own site, the best validation tools for both css and (x)html are at the W3C website. If you want to make the tools easier to to access, then download the webmaster tools in either Firefox browser or Google Chrome.