A requirement for the reporting portion of an upcoming system of mine is that the Y-axis of charts can start at 0, or a defined number, or by letting the chart decide (automatic). This, like many of the requirements for this particular system, is because of the way Excel charts work.
Dynamically setting the minimum axis in a Reporting Services chart can be done by typing an expression in the "Scale", "Minimum" box (for SSRS 2005 and greater only). Note you don't have the benfit of the expression editor:
In the above image I've passed the minimum with the dataset. I'm sure...