Higher-res external monitors under X

[Jesse Sheidlower]

I've asked a variant of this question elsewhere, so I
apologize for anyone seeing it again. To reduce it to what I
think is the simplest form:

I'm running XFree86 4.3.0 on an IBM ThinkPad X23 under FreeBSD
4.8, with Gnome/Metacity. The built-in screen has a maximum
resolution of 1024x768. I would like to be able to plug in an
external monitor and have that monitor display with a higher
resolution, without having to restart X (and thus have to shut
down all my running X apps, etc.).

How can I accomplish this, if it's even possible?

Thank you.

Jesse Sheidlower