Seems to be two options that I see
There is a PCMCIA Video Card that enables two external monitors with powerbooks (
http://www.villagetronic.com/e_pr_vtbook.html)
and
Triplehead2go is VGA ONLY (NO DVI), has a max resolution of 3840 x 1024 pixels (NOT 1200), and treats 2 monitors as one device, so you'd have the doc split etc.
http://www.tgdaily.com/content/view/24937/98/