Populate and sort combobox on userform using VBA

Hi

I am having great difficulty in doing this and would be grateful for any advice.

I have a userform with a combobox (cboExistingSupplier) and a textbox (txtNewSupplier). The combobox gets data from Sheet1, column D. If the user cannot find a name in the combobox to select, he puts a new name in the textbox. This new name will be added to the list in Sheet1, column D. So when the user next uses the combobox, the new name will be shown.

My problem is how to sort the new list in the combobox so that the new name is in the correct place.

Any advice would be much appreciated.

Cheers