I haven't messed with it much, but I don't think there is a way of passing arguments to a script when you execute it via the python window! If I am right, ESRI must have overlooked this one. I think your options would then be to:
1. Hard code the arguments in the script, and run it via the python window.
2. If your arguments are simple, like a single number or something, use the input() method. Example: test = input("Provide a number")
3. Run the script in Pythonwin, wing, etc. where you can specify the parameters.
4. Build a toolbox and use arcpy.getparameterastext() in you code to accept the arguments from the toolbox.