which packages replace fglrx-driver and fglrx-kernel-2.6.18-4-amd64 ?
None yet, but the latest xserver-xorg doesn't work with the fglrx driver. Put your xserver-xorg package on hold before trying to upgrade, and wait until AMD releases the new driver (or even better, use the xserver-xorg-video-ati driver if you have a pre-R500 radeon). Robin