There is a visual editor for Eclipse at
http://www.eclipse.org/vep/ that has been released. There are a couple other Eclipse packages that you need to download and install as well, EMF and GEF that have their own download pages linked from the visual editor page . If you follow the link to the M2 build near the top of the page at the URL I provided you will see the details of what you need to download. Be sure to download the levels matching your level of Eclipse.
I'm running Eclipse 3.0.0 on Linux with an Athlon 3200+ XP and the editor does seem a little sluggish. Filling in all the properties using the properties editors for each object gets rather tedious, but all GUI editors I've seen seem to suffer from that problem.
There's a few articles about Eclipse, including a basic GUI editor tutorial in the Oct 2004 Dr. Dobbs.