Copying text from text boxes

Hello...

I need help with something that looks simple but I don't know how to do it. I have a text box in an excel 2003 sheet where people are supposed to answer a certain question and type text within the txt box. I then want to check if there is any text in the boxes or there is nothing. If there is nothing I want to show a warning to enter any txt in the boxes. My main questions are:

1) I was thinking of selecting the txt box and copy the text in a nearby cell. Then I'll check if the length of the txt in the cell is equal to 0 or not. If it is I'll add a warning message. My missing part is how to select the txt box and then copy all the text within the box and paste it in cell A1 (for example). That would be enough, if someone knows more I'll also be happy with..
2) An advice on how to make that test (copy the txt within the text box and check its length) when someone tries to close the file. Is there anyway of using vba to understand when someone tries to close the file, and then do something else before the file closes?

Thanks a lot for any help. edit: I just realized that I should have posted my thread in the "excel programming" area and not here. My questions involves VBA obviously. Sorry for that.