Different xorg for different configs

[Paul Kaplan]

I know how to use different server layout stanzas in xorg.conf to configure X 
for different situations.  How would I get X to determine whether an external 
monitor is attached to my system at boot time and then call the appropriate 
server layout without any intervention on my part?

I have a xinerama enabled config that works with my external monitor attached, 
but leaves me with a largely inaccessible piece of my desktop when the 
monitor isn't present.

TIA
Paul