I'm assuming slackpkg is used similarly to apt-get. For instance, you type
slackpkg install pkgname
It's not working for some common packages, however (i.e. hping). In fact, it won't work for ANY packages unless they're already installed and I type
slackpkg reinstall nmap
This will take me to a window that looks like the pkgtool command w/ the nmap package in a ncurses window.