Yes, you can easily insert a dropdown calendar into a cell in Excel 2007. Here are the steps:

1. Click on the cell where you want to insert the dropdown calendar.
2. Go to the "Developer" tab in the ribbon (if you don't see this tab, you may need to enable it in Excel options).
3. Click on the "Insert" dropdown in the "Controls" group, and select "More Controls".
4. In the "More Controls" dialog box, scroll down and select "Microsoft Date and Time Picker Control 6.0" (or a later version if available).
5. Click "OK" to close the dialog box.
6. Your cursor will now turn into a crosshair. Click and drag to draw the calendar control in your cell.
7. Right-click on the control and select "Properties".
8. In the "Properties" window, you can customize the appearance and behavior of the calendar control. For example, you can set the default date, the format of the date, and whether the user can type in the date or must select it from the calendar.
9. Close the "Properties" window and save your spreadsheet.

Now, when the user clicks on the cell with the calendar control, a dropdown calendar will appear. They can select a date from the calendar and it will be inserted into the cell.