Changing mouse cursor? Is it possible?

Is it possible to change mouse cursor globally? By changing I don't mean underlying an image ( like Mighty Mouse application) but the "pointer" completely hidden and a new image in place. I know this can be done in the foremost application (without hiding the "pointer") but can it be done when any application is open and with hiding the "pointer" (i.e globally)? For example when you take a screen shot, the cursor changes to cross hair no matter what application you are in; that's what I am looking for.

Thanks

 

With Mighty Mouse, the "pointer" cursor doesn't get hidden. It just puts an image below the "pointer". I want a similar effect expect without the "pointer".