Yes, Spring Rich is built on standard J2SE Swing. It's important to note we exist to abstract developers away a good deal from the complexity of the underlying Swing toolkit (sidenote: some call Swing a framework, the right word for it is "widget toolkit"). The goal of these abstractions is to make it easier to build Swing-powered apps faster and in a consistent fashion -- like core Spring does for J2EE. It is not our goal to support mixing and matching widget toolkits. Swing more than fits the bill, it's the standard, and we believe building on it, not introducing more complexity by trying to support SWT, too.
As some one who builds Swing apps for a living, I can attest that Swing has gotten quite good. It's certainly is and will remain the most mature and complete widget toolkit for Java.
Unfortunately, Swing has always had a bad, misunderstood rap regarding two things: performance and native L&F emulation. In reality performance has been strong since J2SE 1.4. With J2SE 1.5 it's even better. Also with 1.5 we finally get strong native L&F emulation--e.g the windows L&F actually looks like windows.
I would recommend Swing on J2SE 1.5. I can't imagine building a new client with legacy MFC/C++ -- Java is worlds easier as a platform to develop rapidly on, and you're in the middle of a resurgence of java on the desktop.
Spring Rich integrates a number of products, and there are a number we are pursuing integration with now. These include GUI commands (a java.dev project, we leverage their design concepts and contributions in our IoC-configured GUI command framework), JGoodies Forms Layout, JGoodies Looks, JGoodies Binding (we have our own control-to-domain-object binding framework, but collaborate with Karsten in terms of API usage--we also borrow ideas from each other.), JDNC, JDIC, Spin, Foxtrot, Glazed Lists, JIDE (the JIDE team is pursuing JIDE docking integration with our application window/page/view abstractions), InfoNode (another docking framework we want to integrate with), and FlexDock (yet another windowing system.) Re: the windowing/docking integration, it's our goal to make the underlying windowing capability pluggable through a set of well defined application abstractions. This work is in progress now and will reach completion Q1 2005.
Hope this helps! Good luck on your new project!
Core Spring Development Team