Write text from textbox into external textfile?

I have a user form that has a large textbox. I am populating the textbox with the entire contents of a textfile. The user can edit the text in the textbox.

When the OK button is clicked, I need all the data from the textbox to be written back to the textfile and then save the textfile. See the example workbook and textfile attached.

Is this possible?

Excel 2000

Thanks for any help.