I bought the video game Runaway - The Dream of the Turtle. It's a DVD and it installed fine, but when I try to open the game to play it, a message pops up telling me to "Please Insert the original CD/DVD of Runaway 2" when the disc is already in there.

I have a Compaq Presario S6300 NX desktop with AMD/Athlon XP2800+ and I just bought NVIDIA GeForce FX5200 graphics video card. 512MB. Like I said, it installed fine, but I it doesn't recognize the disc in the drive.

Any ideas

You probably have a virtual drive(s) installed yes? Such as Daemon Tools? Even burning software will install there own virtual drive.

Some copy protection schemes look for virtual drives, and refuse to run.