Welcome. This bare-bone little faq details how to get fglrx working on slackware or 64 bit porting.
You can use the internal Slackbuild or the external Slackbuild in order to have fglrx packaged for Slackware.
The internal Slackbuild is distributed within the official ATI installer.
The external Slackbuild is for driver version < 8.37.6.
You can find more detailed information about both of them on the following links.
Internal Slackbuildand for the latest driver patches
Tips and Tricks
Slamd64 - You need to install GCC 3.3 libraries for fglrx. Download and install cxxlibs5. You will also need to install the 32 bit compatibility libraries in /c.