Eclipse has built in SWT support, which is a competing technology to Swing. Not sure about plugins. You should probably try NetBeans, as this has a very good built-in Swing GUI creator, with drag-and-drop. This is often cited as NetBeans' advantage over Eclipse.
I would recommend looking into Rich Client Platform (RCP). RCP is new to Eclipse 3.0. If you are interested check out the tutorials and other information you find here: http://www.eclipsepowered.org/rcp.html