I was unable to find the answer to this question in the software's liturature and was also unsuccessful in this sites FAQ's 1)Sonic PC CD, any attempt to go to fullscreen mode causes the program to crash. I have tried variations from 640X480X256 to 1024X768X32bit and operating systems 98 to XP Will monitor for answers Leo T
The game runs on 256 colors only. Sonic CD also can't work on Windows XP because it doesn't like DOS. Though a Windows program, it could still require some DOS info. In which case, it'd mess up the program, for full screen mode that is. Why it'd not work on 9x is beyond me... you should probibly keep it in window mode.

~ SA Tails