Welcome. This bare-bone little faq details how to get fglrx working on Slackware, Slackware64 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.
External SlackBuild (for driver version < 8.37.6)
|Distribution Neutral Steps|