how can i disable mouse cursor?

Visibility

While disabling the cursor isn't really possible, it can be made invisible.

This can be done with the following code:

Cursor.visible = false;

Locking

Another method, that has a side effect of making the cursor invisible, is to lock the cursor to the center of the screen, this can be ideal when using mouse input for pan/tilt or pitch/yaw type controls, i.e. camera pan/title or spacecraft movements

 Cursor.lockState = CursorLockMode.Locked

More info, including different lockstates and how to use a custom cursor, can be found here: Unity - Scripting API: Cursor

http://docs.unity3d.com/Documentation/ScriptReference/Screen-showCursor.html and/or http://docs.unity3d.com/Documentation/ScriptReference/Screen-lockCursor.html

showCursor show/hides the cursor while lockCursor prevents the cursor form leaving the window.