Saving an NSImage to an image file

FROM : Graham
DATE : Sun Jun 04 20:52:30 2006

I can find a couple of sample pieces to do this, but they are part of 
something more complex and I cannot determine what I need.
So how do I save an NSImage instance (obtained from an NSURL) into a 
file, .tif or jpeg or whatever? Assume I already have a file path for 
the file.