Macbook pro & 1680 x 1050 monitor setting not working

First time posting:

I'm having a problem with getting my samsung syncmaster 2233 to work at its native resolution (1680 x 1050) with my late 2009 macbook pro. It seems to work with all lower resolutions (though the picture is not right, it at least stays on) but when I select the appropriate one my external monitor goes black and flickers on and off every so often.

After looking at other posts on different sites it seems that there was a fix in energy savings to switch the graphics from "better battery" to "high performance" but I cant seem to be able to find these settings. I just updated my software to 10.6.4, so these settings may not be available in the latest software release?

If someone has a solution for this problem please help, its extremely frustrating not being able to use my monitor with my computer.

I've tried all other resolutions and none of them look quite right. I really want to use the native resolution of the monitor because I do a lot of graphic design stuff.

I've also tried looking into the energy saver section in system preferences but the option for better performance with graphics is just not there... I'm attaching a screen shot...

Mirroring is already turned off.... the best resolution im able to get to is 1600 x 1000... once I click on the 1680 x 1050 resolution the external monitor goes black. It flickers, and shows the screen for a couple seconds every so often but mostly stays black.