Matthew, that'll not work if the user backspaces, spaces or use the arrow buttons.
Use this instead:
Code:
Private Sub Text1_KeyPress(KeyAscii As Integer)
'1 to 32 are system keys (del, space, tab, ctrl + V/C/Z, etc.)
If KeyAscii < 33 Then Exit Sub
If Not (IsNumeric(Chr(KeyAscii))) Then KeyAscii = 0
End Sub
It's pretty easy too!