I don't use Slackware as my desktop ... but as far as I'm aware, Gnome support has already been dropped from Slackware. I do like Gnome though and when I did use a Slackware desktop, I used Dropline Gnome. It's installation is painless. The only caveat is that the install is a net-install.What I usually did was to install the base packages to get the Dropline Gnome installer running. Check out
if you are interested. It looks like they've managed to make an installer and ISO you might not be required to do a net-install. Good luck man.