I have installed JavaScript Development Tools Plugin for Eclipse, but i am not able to run or debug a JavaScript Project.
I want to debug using the inbuilt Rhino Interp
Apparently you didn't create a valid javascript project. Depending on your Eclipse version, this is for Juno, go to File - New - Javascript Project.
Javascript projects don't have a "nature" associated with them that let you know in the Project Explorer. Spring, Java, or even Perl projects have this in eclipse. It's a symbol assigned to a project that lets Eclipse know what type of project it is. Java projects have a "J", Spring projects have an "S".