Also, make sure your hard drive has a few megabytes of disk space left. Try uninstalling and reinstalling the game from scratch. Some users have reported their initial install was very slow and a reinstall fixed the problem. Switch to 256 or 'hi-color' resolution. Switch to 640x480 256-color resolution.
Higher resolutions eat more memory, and the graphics take longer to draw.
The game will automatically switch over to an optimized palette so it will look almost as good under 256-color but will run much faster. Make sure your disk is not too fragmented. If your system is several months old and you have never defragmented the disk, you will see noticeable slowdowns in fast-paced programs such as this. If disabling improves speed, you should check your sound card's manufacturer for newer MIDI drivers. This is particularly true if the songs seem choppy and the tempo uneven.