click the line you want to dimension, turn on your "edge filter" then click to place the dimension
edit: works with any filter as long as its not the face filter, obviously, cause if you use the face filter its going to pick the face..lol
And you can use the "e" key on the keyboard to toggle the edge filter on and off.
Excellent! I knew I remembered something about disabling the ability to select faces. That's going to help me out a ton, in the future.
Thanks for answering my noobish question.