I wouldn't use that method myself. I would put a label right above the textbox on the form that holds the "text". If this "text" needs to be added to an output or somesuch, then just join the two during the output process -
Me.Label1.Text & " " & Me.TextBox1.Text
BUT...if your setup really is necessary, you could possibly make use of the length property of the textbox. Since you have the "block" of text at the top of your textbox, you probably know the length. Using the TextChanged property of the textbox, check to see if the length of the textbox is less than or equal to the length of the set text. If it is, reset the text to that text. You also might want to give the users a prompt, as I would find this behavior quite bizzare. Finally, I would also include some code (or maybe there is a property - I don't remember) that forces the cursor to always go to the end of the text when you enter that textbox. That way the users don't begin with overwrite as is default.
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People think it must be fun to be a super genius, but they don't realize how hard it is to put up with all the idiots in the world. (Calvin from Calvin And Hobbs)
Robert L. Johnson III
CCNA, CCDA, MCSA, CNA, Net+, A+, CHDP
VB/Access Programmer