Then you want the patch that is here http://dlh.net/cgi-bin/dlp.cgi?lang=eng&sys=pc&file=gkcdpat.zip&ref=ps
(assuming you have the original CD version and not the version that came with the GK Mysteries set)
It's a zip file, so you'll need something like Winzip to unzip it with.
Here are the instructions from the Readme:
Gabriel Knight - CD-ROM Version
Patch to Update to Version 1.0a
January 10, 1993
This diskette or archive file contains the necessary files to update your copy of Gabriel Knight CD to version 1.0a. This update corrects several problems described below.
PLEASE NOTE: IN ORDER TO CORRECT THE TECHNICAL DIFFICULTIES YOU MAY HAVE ENCOUNTERED WITH THIS PROGRAM, IT WAS NECESSARY THAT WE MAKE REVISIONS TO THE PROGRAM THAT WILL NOT ALLOW FOR THE USE OF
PREVIOUS SAVED GAMES. WE SINCERELY APOLOGIZE FOR THIS INCONVENIENCE.
THIS UPDATE IS FOR THE CD VERSION ONLY! DO NOT USE THIS UPDATE FOR THE FLOPPY VERSION OF GABRIEL KNIGHT!
If you are running the DOS version of Gabriel Knight CD, copy these files into your game directory (e.g. C:\SIERRA\GKCD), and then from
within that directory, type GKCD and press [Enter] at the DOS prompt.
To run the game, type GKCD and press [Enter] again.
If you are running the Windows version of Gabriel Knight CD, copy these files into your game directory (e.g. C:\SIERRA\GKCD). If you did a Medium or Large installation, this is all you need to do.
If you did a Small installation in Windows, you will need to follow these instructions to install the patch:
1) Start Windows and click on the Gabriel Knight icon once to highlight it.
2) Press [ALT]-[ENTER] to bring up a Program Item Properties dialogue box.
3) In the Command Line box, you will need to change the path of the SIERRAW.EXE file to point to the game directory on your hard drive. For example, if your CD-ROM is drive D: and you installed the game to the default \SIERRA\GKCD directory on your C: drive, the Command Line would look like this:
To make the patch work with a small install, change the above line to this: