Dispersion is when different wavelengths refract differently. I guess the most obvious case of this is a rainbow.
Real sunlight is a spectra containing basically an infinite number of wavelengths at once, and each of the different wavelengths will refract slightly differently... i.e. when a sunray hits a surface, one would (in principle) need to trace an infinite amount of rays around the scene to get the "real" effect.
Computers aren't very fond of doing an infinite number of things - at least not if you want them to ever finish. So there are several ways to simulate this w. various techniques.
The technique we will be using here is a very low-tech one - we simply render the scene multiple times with slightly different IOR's, colorize each of the renderings based roughly on the "color" of that wavelength, and combine the result. Et voila, we have a dispersive render.
To aid in this I slapped together a little piece of maxscript. Go to your Maxscript menu and choose "Run Script". A small dialog will pop up with some options.