Were you flipping through these while on 1680x1050 resolution? They don't do anything for the native resolution, they set how the image is scaled when using a non-native res. Say you set it to 1024x768. The 1:1 setting will display the image at 1024x768, so you will have the image centered in the middle of the monitor with black bars on all sides. Fit would stretch the image out in all directions to fill out the entire monitor. Aspect keeps the image in its original aspect ratio but stretches where it can, so a 1024x768 image would be stretched vertically, and you would just have black bars on the sides of the image.
At least that's from what I remember when I first got my 2005, I run everything at 1680x1050 so I don't really pay any attention to those settings.