I couldn't find anything under an apt-cache search, so searched it on
the Debian website and found a number of nvidia-related packages that
contain this library file. All good.
Yep... I've got "nvidia" driver installed.
sm01@stt008:~$ dpkg -S libGLcore.so.1
nvidia-glx: /usr/lib/libGLcore.so.173.14.09
nvidia-glx: /usr/lib/libGLcore.so.1
Let me check:
sm01@stt008:~$ dpkg -l | grep nvidia
ii nvidia-glx 173.14.09-5 NVIDIA binary Xorg driver
ii nvidia-kernel-2.6.26-2-amd64 173.14.09+3+lenny1 NVIDIA binary kernel module for Linux 2.6.26
ii nvidia-kernel-common 20080825+1 NVIDIA binary kernel module common files
But I have installed those just because my VGA card is nvidia-based.