http://www.devel.lyx.org/changetracking.php3
(not yet implemented in the stable 1.3.x series, but I think there's a patch around).
Johnathan Burchill tweaked this patch and made it work with 1.3.2 .. you can download it from his website at:
http://members.shaw.ca/jkerrb/computer.html
I've used this with 1.3.2 and it works great.. I haven't tried it with 1.3.3...
nirmal
