Hi desert rat..
If you don't have access to a board simulation tool such as Hyperlynx, you can search the web for "IBIS Viewers". I have used a couple of different ones, they all behave about the same. I prefer the one from Mentor, it's very intuitive and I was up and running within minutes. When you create your VI curves for the pull-up (device driving high), use "Ground relative" instead of "VCC relative". The curves will be like you're used to seeing in data books. For the pull-up at ground relative, use the positive voltage, negative current quadrant. For the pull down, use the positive voltage, positive current quadrant.
