Sory to state the obvious but you did say you were new...
If the lens has a Nikon mount it will fit the D80. Sigma made that same lens in various mounts for Canon and so on.
It is kind of a cheap lens. Seems after springing for the nice D80 you'd want some first rate lenses. I would much rather buy a used Nikon than a low-end Sigma If budge is an issue buy used lenses.