Sorry, what Im looking is for a plugin for other project management software, since MS PROJECT has been banned in my company (go figure), so I can import projects, lets say, from GANTT PROJECT as an example.
The answer is "No, there's no Out-of-the-box integration between HP PPM Center and other Work plan management tools (such as "OpenProj/ProjectLibre")".
The main issue if you want to create your own integration is that, as of today, there are no officially supported interface in PPM that will let you build such an integration (i.e. web services to manipulate Project & Work plan data, either SOAP or REST).
The integration between PPM and MS Project uses a .Net add-in in MS Project for client side work plan manipulation, and the interface to exchange data between that add-in and HP PPM Center is not open for public use.
Of course, one could always analyze the traffic between the .Net add-in and PPM to reverse-engineer it and build a plugin for another application around it (it's plain XML over HTTP, so using Fiddler should tell you anything you need to know), but the problem is that this interface is not open for public use, and any solution built on this would NOT be supported by HP, and might result in undesirable side effects that are not covered by support agreement.
There might be a better work plan management official interface in a future PPM release, but as of now, that's not yet the case.