If you don't want to change your regional settings, or enter the date
manually, you can use VBA to automatically update the date. One way:
Put this in the ThisWorkbook code module:
Private Sub Workbook_BeforePrint(Cancel As Boolean)
Dim ws As Worksheet
For Each ws In ActiveWindow.SelectedSheets
ws.PageSetup.LeftHeader = Format(Date, "mmmm d, yyyy")
Next ws
End Sub
Change LeftHeader to CenterHeader or RightHeader if desired.
If you're unfamiliar with macros, see
http://www.mvps.org/dmcritchie/excel/getstarted.htm