What do I need to do to get a package that I can submit to the Ubuntu Software Center?
It's very hard to tell from your question what you already know, so I assume that you:
As far as I know, the QT Creator is not able to create debian packages to submit to the Ubuntu Software Center.
QT Creator is able to create debian packages for Maemo5 (see here). Looking through the discussions on Maemo, it seemes that this process is not easily changeable, but maybe you can start from there.
If you are not fixated on QT Creator, you can simply use it to create you code and then follow the Ubuntu Packaging Guide to create your debian package.
The actual submission to the Software Center is described here.
For future questions I would suggest you write in more detail what your actual problem is.
You can do this with an additional rule in the makefile generated by qmake:
Now you can create your package calling