Well, there are three cables, but you only need to look at two of them, both of which you mentioned in your title.
Now, I'm not sure what the iBook cable was, but take a look at the following picture and tell me whether you need a cable that has a connector like the one on the left or the one on the right:
If it's the left one, then you need the mini-DVI to VGA adapter. If the right one, then the mini-DVI to DVI adapter. Both cost the same and are available at both your local Apple store and at many online stores as well. :black: