RMS should also say "Don't buy from Intel or Nvidia"
Anyways, it would help to know a couple of items.
First, which kernel version you have?
Second, what distribution you are using?
If you are using a Debian based distribution, like Mepis, you might need to run dpkg-reconfigure xserver-xorg and force the fglrx driver to load, as well as set a proper resolution and refresh rate, as well as the PCIe location of your card.
Third: did you install Fglrx from your Vendor, or did you install it using the download from the AMD site?
If you installed from the AMD site, you might wind up with something like this:
Click on the picture for the larger version. Here, it is shown that while the ATi driver is installed, the 3D is actually being handled by the Mesa OpenGL driver... which is slow.
What you want is something like this, where the Fglrx driver is loaded.
Another tip is to check Kinfocenter's OpenGL tab and see what the output is. If KDE throws up an error that OpenGL couldn't be accessed... well, there you go. Driver wasn't loaded properly.