Will my ibook 12" 1.2ghz support the Dell 20" widescreen monitor at its normal res (1680 x 1050)?

I have found that I can hook my ibook up to a 19" Dell LCD that I have and run it at 1280x1024, without problem. I can even do spanning without a problem. However, what about 1680x1050 on the 20"?

Also, will it slow my system down to render to a larger screen? I do have 1.25gb ram.