read your /var/log/Xorg.0.log then... it should say something about "failed to load fglrx" no doubt. Meaning that there is a problem with the kernel module not being built or installed properly. After running module-assistant, make sure run "depmod -a" otherwise you might have problems. Also you could just try "modprobe fglrx" and check "dmesg" output to see if it loaded. I am using Feisty with no problems with this driver.
Desktop: Core 2 Duo E6400, P965 chipset, 2GB, Radeon X1900GT 256MB, Ubuntu Edgy (am64)
Notebook: NEC LaVie RX, Pentium-M 1.5GHz, i855 chipset, 768MB, Mobility Radeon 9600 64MB, Ubuntu (Dapper)
HTPC: Shuttle ST20G5, Athlon64 3000+, 1GB, Radeon Xpress 200 chipset, Radeon X550 128MB PCIe, Gentoo (amd64) [+Debian(sid) +Ubuntu(breezy)]