"Workspace in use" from Eclipse most commonly comes from one of 2 things:
1. The workspace is, in fact already in use by another copy of Eclipse
2. The metadata containing the workspace lock is out of sync. The only cure for this I know of is to go into the workspace directory and delete the entire .metadata folder.
If you really need something lighter on memory, pretty much all the major
Java IDEs are CPU and memory pigs. I have a 200MHz/98MB machine that occasionally I do work on, and there's no way any of those will run there (for one thing, there's not even enough RAM to run X Windows). On that machine I quite happily use Emacs with the JDE plugin. Not as slick as the GUI IDE's, but decent for Java development considering the limitations of the platform.
Rumor has it that the vi editor has something similar, but I've never seen it.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.