The recent update of Parallels to build 8.0.18483 (Revision 860857, March 30, 2013) fixed this for me.
openSUSE 12.3 now runs.
Edited: Parallels tools now installs, but something is wrong with the X11 configuration for opensuse 12.3
(12.2 is fine). Also the drivers prlvideo and prlmouse were installed with wrong permissions (not executable)
But after fixing that, some more work seems to be needed on xorg.conf...
(I didn't succeed in getting correct mouse behavior yet)
Edited again: OK, so openSUSE 12.3 is not yet supported in the latest Parallel tools; comparing 12.3 with 12.2, the error is that /var/log/Xorg.0.log shows that the display and keyboard get set up correctly, but that when the mouse is set up, the prlmouse driver never gets loaded in 12.3 while it does in 12.2. The entry in /etc/X11/xorf.conf.d/50-prlmouse.conf is the same in both 12.2 and 12.3, but somehow prlmouse is not looked for or found in 12.3
Last edited: Apr 13, 2013