Fglrx 12,6 is in the Debian stable/Wheezy repo Fglrx 13.4 is in the Debian testing/Jessie
Download from AMD:
The directions given on the Debian page have been changed reciently and are no longer correct, the fglrx package build for Debian has not worked in a long time.
for a first time install:
./name.run --force then aticonfig --initial -f then reboot