I have solved the problem with resolution
Try the following:
Option "SecondMonitorHorizSync" 31-90
Option "SecondMonitorVertRefresh" 58-75
in your "Device" section.
Wenn you have still the same problem(resolution from LCD), search linux-dell-laptops group on groups.yahoo.com
For second monitor's synchronisation I think that we must wait for the new driver from NVidia ;-(