VGA output is enabled by default in X. To get toggleable VGA output via Fn-F7, add the following line to your Device section of /etc/X11/xorg.conf:
Option "BIOSHotkeys" "on"
tpb will also show the current status of this toggle.
I had an interesting issue where on some external monitors, the output was... squiggly... unless X was started with the monitor attached. This issue can be solved by switching to the monitor once it's connected.