The lower the f-number (f2.8, f1.8,f1.4) means that more light comes into the lens. The reason they call them "fast" lenses is because it allows you to use higher shutter speeds without bumping up your ISO. Also the viewfinder is literally brighter because the lens is always opened up to the "widest" opening or smallest f-number.
The data from your pictures states that your settings were f5, 1/125th, ISO 400 at about 100mm. I see a good exposure, great color, and little noise. The only thing is that that runner was moving fast! So 1/125 shutter is not going to freeze him no matter what lens you use.
The camera doesn't know you want the runner to be the "focus" of your picture and that you don't care if the people in those stadium seats are properly exposed. Your D60 is trying to account for the entire scene and not just the runner! So go into S (shutter) exposure mode and set your shutter higher than 1/125 to freeze the action.
Honestly these pictures are very good from a technical point of view. I think you'd be wasting your money with a D90 because you'd probably make the same mistake.
Again jmichael99 really really just learn how to use your D60 first. Keep the questions coming, that's why we're here!
