If you'd like to only have the calendar appear when you need to pick a date,
you can use this routine.

YourTextBoxName is the name of the box that will hold the date

YourCalendarName is the name of your calendar.

First, place the calendar where you want it to appear on the form.

Next, select the calendar and goto Properties--Format and set Visible = No

Then place this code in the form's code module:

Private Sub Form_Load()
  YourCalendarName = Date
End Sub
 
Private Sub YourCalendarName_Click()
  YourTextBoxName = YourCalendarName
  YourTextBoxName.SetFocus
  YourCalendarName.Visible = False
End Sub
 
Private Sub YourTextBoxName_DblClick(Cancel As Integer)
 YourCalendarName.Visible = True
End Sub

Now, when your user DoubleClicks on the textbox where the date will go, the
calendar will appear. The date is picked, and the calendar disappears!

There are several good website to get such tools so that you don't need to
reinvent the wheel.  whatever you do stay away from activex control for this,
they are a headache and cause versioning issue.  Below are two great calendar
pop-ups.  I have used both from several years now.  They are robust (do not
fail/crash)...

http://allenbrowne.com/ser-51.html
http://www.lebans.com/monthcalendar.htm