What you can do is you can download node.js from node.js, download the package and follow the installation instructions on the screen.
If using a Windows, the node.js package comes with its own interactive command prompt which you can open. To run a js file on windows, open the windows command prompt, type in node, then the name of your file e.g. test.js. Node.js should run your file.
If using a Mac, the node.js package runs through the terminal application on the mac. To run a file, type in node, then the name of your file e.g. test.js, node.js should run the file.
Aptana Studio 3 has the ability to open the terminal inside the IDE itself. Save your file in Aptana Studio and follow the instructions to run a file on the mac.
By the way, keep your files labelled in lowercase letters, I tried using Uppercase for the first letter and it did not work.
Hope that helps.