Delete or rename the file <path-to-game>\DATA\MOVIES\LEGALS.BIK
The game lags terribly in modern operating systems, such as Windows 8 and 10. In order to fix this, you have to use "dgVoodoo 2" by Dege. Follow the instructions in this video (Dark Ruler fix). The game will now run at 60 FPS in Windows 8 and 10. (Note: the program may be detected as malware; the developer of the program (Dege) asserts that it's merely a false positive).
8. Replace the letter X:\ with the respective folders for each disk, e.g.
Make sue you do the same for the Movies files as well.
9. Save the file and run the game.