This must be very frustrating.
I'm still new, with only 6 months experience using eclipse and SWT-Designer, but I would guess your problem is probably more to blame on your system.
If you're desperate enough, here's a few things to try:
1. In Eclipse, from Window menu select Show View, Error Log. Examine this log- you might be surprised how many scary things are in there! Right click in the log, select Export Log and ask Eric if you can send it to him. The guy is a wizard and nailed a bad problem for me that way.
2. Before starting eclipse, try deleting everything in eclipse's Configuration folder except for the config.ini file.
3. Try installing on another machine.
4. Try installing everything from scratch.
5. Try getting rid of all of the various versions of Java that may have accumulated on your machine. It's easy to have a lot of these. This is a real long shot, but I have read about and experienced various problems related to multiple versions of java. So, after getting rid of them all, ask your developer which one to install and reinstall eclipse and swt-designer from scratch too.
6. Another long shot, but look at environment variables.