how to catch mouse x and mouse y on the screen?

I know in the ActionScript I can get the mouse x, with stage.mouseX, or simply mouseX, and stage.mouseY, and mouseY, for obtain the values of this mouse position, how can I get this values in C# or JS for Unity?

Input.mousePosition

http://unity3d.com/support/documentation/ScriptReference/Input-mousePosition.html

It is a vector 3 value. You can get the x and y co-ordinates out of that.