For an LCD native and maximum resolution are one in the same as far as I know. Never seen them be different anyways.
The resolution options are going to vary depending on the monitor you have installed. If you are currently using a 4:3 monitor, you will not have an option for 1680x1050 since this is a 16:10 (yeah, most wide screen comp LCD's are 16:10, not 16:9
) resolution. This option will be there after you install the new monitor.
You might also want to look at the Dell 20" wide screen monitors. I have the 2005 which has been awesome, and I believe it is the 2007 out now which I have heard is great.