Custom resolution for Ubuntu VM running in VirtualBox on Linux

So, I've got a Ubuntu server linux box where I run VirtualBox VM's, including an Ubuntu Desktop machine that I remotely display on my Windows box. (Yeah, I know, confusing and overly complicated.) Anyway, when running Gnome on the Ubuntu desktop, the maximum resolution it would give me was 1360x768. Since I have a 1920x1200 monitor on my Windows machine where I run my X server, I wanted a bigger Ubuntu desktop.

The most useful post I found was this: http://www.ubuntugeek.com/how-change-display-resolution-settings-using-xrandr.html

I ran the following commands:

1. cvt 1680 1050 -- get a X modeline similar to "1680x1050_60.00" 146.25.... (more numbers)
2. xrandr --newmode {output of the previous modeline}
3. xrandr --addmode VBOX1 1680x1050_60.00 (causes the X display to flash)
4. Use System > Preferences > Monitors to pick my new resolution

Voila. Easy, peasy. Works great now.