Huh... I type in fglrxinfo into the console, and I get back information stating that I'm using the driver:
I suppose this means that I've been using the driver all along since installing it... and that the "dpkg-reconfigure -phigh xserver-xorg" line fixed the driver? I hope this is the case!
display: :0.0 screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: ATI Radeon HD 4600 Series
OpenGL version string: 3.2.9756 Compatibility Profile Context
If it is, then problem solved! If anyone else has this problem, then I recommend typing "dpkg-reconfigure -phigh xserver-xorg" into the console after entering the recovery root shell.
... assuming that this is confirmed to be a viable solution, that is.