[Doggie]

Requirements: Visual Basic(of course), Listbox control, textbox and command button

Listbox is where the item will go, Textbox is the item text and command button to add it to the list

Under the textboxes Change event add

Private Sub textboxname_Change()
    If Text1.Text = "" Then
        Command1.Enabled = False
        Else
        Command1.Enabled = True
    End If
End Sub

If Text1.Text = "" Then <== This is saying if theres no text in the textbox then it will make the command button disabled

Under the Command button Click event

Private Sub Command1_Click()
    List1.AddItem Text1.Text
End Sub

List1.AddItem Text1.Text <== Simply means add item to the list with the text in the textbox

Simple