The base compiz package is include with Slackware but you need to install the other companion packages to really make compiz useable. Get them over at
www.slackbuilds.org
Install them in this order...
1. compiz-bcop
2. protobuf (optional but recommended)
3. libcompizconfig
4. compizconfig-python
5. compizconfig-backend-kconfig4 (optional)
6. ccsm
7. compiz-plugins-main
8. compiz-plugins-extra (optional)
9. compiz-plugins-unsupported (optional)
10. emerald (optional)
11. emerald-themes (optional)
12. fusion-icon (optional)