quesswho, I had a tough time figuring out the focal distance too. I never really got it working right, but I did find a couple of web sites that have a Depth of Field Calculator, you can find that at:
www.shuttercity.com
It seems that the film format has a lot to do with calculating DOF, and it does change quiet a bit depending on the film type you put in the calculator.
But I think the biggest thing is matching the camera's Focal Length with the F-Stop, Focal Distance (I think) is going to be the distance from the camera to the main object. The only problem with that is coming up with an accurate way to measure the distance.
Hmm... I think it might be time to take another look at Dr. Geep's measuring tutorial:)

Well, I'll keep you all updated on the progress of things:)
Oh, and quesswho that's a good looking image!

amon_g