Well, I installed only WindowTester, not RCP Developer. But I think RCP Developer probably comes with WindowTester. But other than that, I did pretty much the same things you did.
When you go into the Preferences->WindowTester->License page, what does it say under the "License" Heading? Is your evaluation period expired? Are you not registered for the WindowTester portion under the RCP Developer install?
That's all I can think of, hope it helps