Shawn, this is really tough for me to answer since all the different brands of jigs are set up differently. Dovetails are not my strong suit either. In general the amount of your offset should equal the diameter of your dovetail bit. This is assuming you are going for equal size, equal spaced dovetails. Your jig should have a 90 degree reference mark or guide of some kind on it. The vertical board should be a good enough reference to square off of. I guess for anyone to give you the correct answer they will need to know the brand of jig you have. If you are not sure, post a photo of it. Sorry I can't be of more help on this one.
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"