External Monitor as Primary/Default Display

I recently installed Lucid Lynx on my Dell Inspiron 9400. One niggling annoyance was that the Dell's LCD screen was the primary display, whereas I wanted my external monitor (BenQ T2200D via DVI) to be the primary display.

Ultimately, the solution was simple:

1. run the NVidia X Server Settings tool (gksudo nvidia-settings)
2. in the X Server Display Configuration I made sure the Dell's display (Seiko) was disabled
3. when saving to the X Configuration file, i.e. /etc/X11/xorg.conf, I chose not to merge with existing file
4. restart X