i don't understand if with GWT designer i can build web (html) application. Thanks
Windows builder PRO published and supported by google. Window Builder was a paid software until google bought it. Now window builder supports GWT, Ext GWT and smart gwt design. And I think it is very good to design GWT, GXT windows.
To Add window builder to eclipse;
Eclipse 3.6 (Helios): http://dl.google.com/eclipse/inst/d2wbpro/latest/3.6
Eclipse 3.5 (Galileo): http://dl.google.com/eclipse/inst/d2wbpro/latest/3.5
Eclipse 3.4 (Ganymede): http://dl.google.com/eclipse/inst/d2wbpro/latest/3.4