I'm staring at two of these monitors right now (sadly hooked up to my PC instead of my G4, but that's another story).
The Dell 2001FP has S-Video, Composite Video, DVI-D, and VGA (RGB) inputs. There's a button on the front to cycle through all four inputs. It can also do picture-in-picture with one computer input and one video input (e.g., DVI and S-Video, but not DVI and RGB).