Our date picker is old, unmaintained, and there are a lot of good date picker for jquery. This bug will decide which datepicker we will use and keep track of the work
Owen has made a suggestion to use jQueryUI datepicker for this.
I am adding a link to bug 5778.
In fact my work on Bug 5481 has already done all the work to replace the current calendar widget with the jQueryUI one.
*** This bug has been marked as a duplicate of bug 5481 ***