Editing programmatically a TextBox in VB 6.0 and/or VB.NET 2003

Hello there,
I have a problem and I need help. My problem is: I have a TextBox and a Button controls on a Form. The TextBox displays a text and after I place the cursor anywhere in that text, when I hit the Button, a pre-programmed text (coded in Button_Click event) must be inserted at the cursor insertion point in the TextBox. Knows anybody how to do this in VB 6.0 and/or VB.NET 2003? Thanks in advance for any suggestion.
Stefan (psbruciu@yahoo.com)