It actually isn't as hard as you would think. I'm not sure exactly the difference between IPB and vB (I mean, I know the differences, I just have never used vB before), but if you edit the main includes (header and footer) first, then work your way through the other pages, you should be able to do this with xhtml / css / basic php knowledge. I was able to code skins for Wordpress after trying it once. It is basically editing someone else's design to fit your design.
HTMLGuy