The TaskBar window's class name is Shell_TrayWnd. Normally just one window of this class exists in the system.

You can find it either by using FindWindow function:

DECLARE INTEGER FindWindow IN user32;
	STRING lpClassName, STRING lpWindowName

hWindow = FindWindow('Shell_TrayWnd', Null)
? hWindow

or enumerating child windows for the Desktop:
http://www.news2news.com/vfp/?example=27

After obtaining this handle use ShowWindow function to show or hide the TaskBar:

DECLARE INTEGER FindWindow IN user32;
	STRING lpClassName, STRING lpWindowName

DECLARE INTEGER ShowWindow IN user32;
	INTEGER hwnd, INTEGER nCmdShow

hWindow = FindWindow('Shell_TrayWnd', Null)

= ShowWindow(hWindow, 1) && show
*= ShowWindow(hWindow, 0) && hide