Other than follow my standard advice, I would suggest playing the later stages of the game on normal speed.
Standard Advice being:
1) Make sure you have the latest patch for the game.
2) Rename the AVI folder to AVI_back
3) Set the color depth to 16BIT
4) Turn off everything in the background like E-mail/ICQ/Messenger, Virus protection and everything in the system tray beside the clock.
5) Update your Windows, update your Video card drivers and audio card drivers. Then repeat steps 1-3.
Standard Advice being:
1) Make sure you have the latest patch for the game.
2) Rename the AVI folder to AVI_back
3) Set the color depth to 16BIT
4) Turn off everything in the background like E-mail/ICQ/Messenger, Virus protection and everything in the system tray beside the clock.
5) Update your Windows, update your Video card drivers and audio card drivers. Then repeat steps 1-3.