To write Qt applications using Python, you need PyQt. To integrate Python, PyQt, PyDev, and Eclipse, you need to do some installation work and set things up correctly. You should find a reasonable starting point in this blog article: Setting up IDE and creating a cross platform Qt Python GUI application. This doesn't allow you to design your Qt UI by dragging and dropping controls. To get that, you could use Qt Designer to "draw" your UI, and then use some tools that come with PyQt to convert the saved design to Python code. This you can then edit and interface with in Eclipse. There are articles on that here, here, and here.
There are also other IDEs that you may want to check out:
See also: http://stackoverflow.com/questions/472021/what-ide-is-good-for-developing-pyqt-apps
(Apologies for not providing links to Qt Designer and Qt Creator – I couldn't find canonical ones. Check out qt.nokia.com and find them there if you want.)