If your card is not a 8x card, powerstrip should help you. just install the trial, add the resolution from powerstrip and you should get the option.
Like I said, you may need the 158 drivers to make my suggestion work. It's specifically stated in the 158 release notes. Also, with the nvidia control panel in 158 you can add HD timings and that should give you your resolution as well.
I've tried the beta 160 drivers and it seems those drivers will not only allow you to add specific timings but will underscan/overscan on the fly, at least this was the case with component out.
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