External monitor for iMac-ATI Radeon X600 Pro graphics processor

After upgrading to Leopard, installing a 500 giga external drive for effortless time machine backups, and a 2.0 gb ram expansion to 2.5, this week I connected an outside monitor to my iMac (a 20 inch Samsung 2043 NWX with a pixel resolution of 1680 by 1050).

It works great.  Here is the problem:  As my iMac only has display mirroring capabilities (it does not have extended desktop that is available in later models), I cannot turn of the built in display, nor can I toggle between the two.

There is a third party patch that claims it gives my iMac extended desktop, but I do not like to install third party patches on my iMac.  Heck, at this point I'm not even sure that with extended desktop I could turn the internal display off to begin with.

The native graphics support card is quite capable:  ATI Radeon X600 Pro graphics processor using PCI-Express and a maximum resolution of 2048 by 1536 pixels.  The status shows it is presently supporting two displays simultaneously:  One at 1440 by 900 pixels (my native iMac display), and another of 1680 by 1050 (my 20 inch Samsung).

I tried dimming the display but the control is disabled whilst on video mirroring mode.  I tried playing with the internal monitor set up but I cannot set the display to zero using this option either.

Let me know your thoughts please.

Best regards, Roberto A. Lovato