I don't use slackware by myselfe i'm on archlinux 64 bit so i don't know your system packaging. Anyway, on archlinux, you have to install three graphics related packages to get a game in wine running: nvidia, nvidia-utils and also lib32-nvidia-utlis. If i don't install the lib32-nvidia-utlis package i get an error. Maybe something similar is happening on your machine. The glxgears error is something i get too without any negative effect i know about. -- Andy