When you say 'develop portlets', there are a number of different ways to write portlet applications and the specific IDE has little to do with it.
Personally I use Spring Portlet MVC, which is working out quite nicely, and yes, I use Eclipse for development. However, you can use Struts Portal Framework, JSF ....
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Get your hands on the portlet sample application (I think it is a part of Spring2 now anyway so yuo could just get your hands on that) and go from there. I use ant to build the war files to deploy the portlet applications, so again, the IDE is of little importance.
If you stick with the JSR168 spec (which Spring adheres to) then your portlets should deploy on any container that meets the spec, including JBoss, Liferay....