Probably not. Slackware is for Intel x86, Alpha and Sparc CPU architectures only.
You can try using the Slackintosh distribution, but I have heard it's pretty limited:
You are probably better off using Yellow Dog Linux, OpenBSD, or NetBSD for now.
On the other hand, if you'd like to build a version of Slackware for PPC, I am sure a lot of people could be interested...