I'm not exactly certain what you are trying to achieve with the combo box, but you can try Active X controls on the "ToolBox" icon.
There are a lot of controls that you can choose a particular type of calender function from. Some calender functions will look like a text field with a drop down arrow, that when you click on it, it opens out into a calender that looks like the Date/Time on the Start menu of your PC.
Yes, put the combo box on your form as well as a calendar control. The only time I've done this is when I hide the calendar but I imagine it will work either way. Usually to show the calendar I code a mousedown event for the combo box to show the calendar control and then code a click event for the calendar to put the date selected into the combo box and then hide the calendar after the click. Sort of like so
private sub comboBox_mouseDown()
calendar.visible = true
private sub calendar_click()
comboBox.value = calendar.value
calendar.visible = false