Debian has made the transition to the X.org installation of the X11 Window system. If you're running sid/etch you are able to upgrade.
The friends at debian-administration has written a guide for you to make the switch. And before you do, remember
Before starting the upgrade to X.org it's important to do two things:
* Switch to a console as a paranoid safety measure. If something goes wrong, or X gets restarted you don't want to leave your upgrade in an inconsistent state.
* Take a backup of /etc/X11 in case you experience problems.