macbook mirroring on 37'' vizio 1080p

I just bought a 37 inch vizio hdtv and want to use it as a macbooks primary monitor. I used to do this on my 27 inch 720p tv with no problems however now it is only puting up aprox a 20'' picture in the middle of the hdtv when mirroring and mostly fills it when extending the desktop. Does anybody know how to solve this problem? I dont care if its mirrored or if i use the macbook as a desktop as long as i have the primary display be the telivison. Any Ideas?

Thanks

Try the clamshell approach. Boot up with the external monitor attached. Then close the lid. Leave the lid closed, and wake the Mac up with an external keyboard or mouse. (If Bluetooth, you will have to enable the wake up function) When the Mac wakes up, it should automatically adjust to the optimum resolution for the external monitor. Also, you should check your HDTV instructions for automatically adjusting input to wide screen format.

i see Switch Res has just upgraded altho not for SL. If u are on Leopard it might be of help sorting Resolutions. Go into Sys Prefs/Displays and drag menu bar onto Ext Monitor to make it the Primary.

http://www.macupdate.com/info.php/id/8355/switchresx