In case you aren't doing this for personal education, but for a real project, there are numerous DateTextBoxes with popup calendars available. They will not only save you time, they have been tested, documented and used in the field. Some are much more feature rich than what you might construct. You can see them at this site's Control Gallery, www.123aspx.com, and www.411asp.net. Mine is
Peter's Date Package. Its popup calendar replaces Microsoft's calendar control with one that doesn't require post backs as you click on it.
--- Peter Blum
Creator of Professional Validation And More Suite, Peter's Date Package, and Peter's Polling Package
www.PeterBlum.com