Tweaker, try:

Code:
Dim yourCharacter as string
bigTextBox.Text = bigTextBox.Text.Replace(yourCharacter & ControlChars.NewLine, "")
You can set yourCharacter to whatever you want and then the code Replace will find it (along with the line below it) and replace it with "", in otherwords nothing, so it will delete it.

Also, dbasnett has a point with using listboxes. What exactly are you trying to do with this list of numbers?