The vast majority of 7th Guest crashes are caused by memory problems.
DON'T change the application's preferred memory size to anything other
than the suggested memory size (2300 k), or it will crash!  If virtual
memory or the Modern Memory Manager are available on your system, turn
them off and restart your Mac before starting the game.

If you are running 7th Guest on a Power PC, try using the PPC patch from
<ftp://www.cybout.com/cyberian/files/>.

Because the 7th Guest writes saved games into the application file, a
crashed game often causes the user to lose his or her saved games.
To recover saved games from a crashed copy of 7th Guest, rename the
original 7th Guest folder, then install another copy from the CD-ROM.
Run your new copy through the opening sequence, then before playing
anything, save a game at the ouija board.

Now use ResEdit to recover the original 7th Guest application file within
your renamed 7th Guest folder.  This will create two files, "T7GMac" and
"T7GMac(damaged)".  Open and allow verification of the recovered T7GMac
file.  Locate the resource labelled 'T7SG'.  Copy the entire T7SG resource
by selecting its icon and using the standard Edit menu functions, then
close the recovered T7GMac application file.

Now use ResEdit to open the newly installed copy of the 7th Guest
application.  Paste the copied T7SG resource into the application file
so that it completely replaces the existing T7SG resource; use the
same resource ID as the one you're replacing.  Save the file, quit
ResEdit, and run the new copy of the 7th Guest; the ouija board should
point you to all your old saved games.

[Thanks to Simon Boocock for this emergency surgery procedure.]