A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Pretty easy to fix, luckily.
Put an apostrope (ie, single quote) before each of the dates.
For example, instead of entering 4/16/2009, enter '4/16/2009
That tells Excel to treat the information as text rather than as a number or date. Excel won't display the apostrophe and won't try to be smarter than you about how the dates are supposed to be formatted. It'll let you be Emperor of the Chart. ;-)
Steve Rindsberg PowerPoint MVP