Shawn --
There's no way of setting a Finish date in an Activity plan, as I have
stated previously, short of entering tasks with Durations. So, I suspect
you will just have to work around that limitation.
Regarding your use of the Resource Plan, I'm still puzzled as to what you
are trying to accomplish. Are you saying that you do both of the following:
1. Assign each resource to tasks in the Activity plan.
2. Assign each resource to a Resource Plan attached to the Activity plan.
Given the fact that #1 above assigns each resource automatically at 100%
Units, then doing #2 as well will show the resource as overbooked in every
time period. Anyway, just trying to figure out what you are doing with
that, but I know this was not your original question. See the two sentences
again for the answer to your original question.
Hope this helps.