You should use the ShowWindow api function to hide the taskbar.
Code:
Declare Function FindWindow Lib "user32" _
Alias "FindWindowA" (ByVal lpClassName As String, ByVal _
lpWindowName As String) As Long
Declare Function ShowWindow Lib "user32" Alias "ShowWindow" _
(ByVal hwnd As Long, ByVal nCmdShow As Long) As Long
Public Const SW_HIDE = 0
Public Const SW_SHOW = 5
Dim tray
Dim trayShow
Usage
Private Sub Command1_Click()
'Hide
tray = FindWindow("Shell_TrayWnd", vbNullString)
trayShow = ShowWindow(tray, SW_HIDE)
End Sub
Private Sub Command2_Click()
'Show
tray = FindWindow("Shell_TrayWnd", vbNullString)
trayShow = ShowWindow(tray, SW_SHOW)
End Sub