Hi i dont understand exactly your question but rich client is something more usable and more responsive than HTML (IMHO) for client side usage. there are some definition about Rich client , but all of them have one similar fact : a more responsive GUI for client side -and cross useable in web browser / desktop application- there are some Rich client frameworks like : Micromedia Flex, Bindows, MS XAML,eclipse platform Mozilla XUL,... you can use any of them for your purpose .
I think John's seen something about the Eclipse "Rich Client Platform." This is just another name for writing GUI apps using a layer on top of SWT (the Eclipse cross-platform window toolkit.)
If you use RCP/SWT, your apps will (in theory) have more of the platform's native look and feel. If you use Swing, then you'll be using something that's more industry standard and far better documented.
If anyone tells you SWT/RCP performs way better than Swing, tell them to prove it to you, because they don't know what they're talking about.