>how to hide the button of a program on the task bar ?

See Message#496306. With VFP7 this code is shorter, because any form has HWND property, so you do not need to determine it:

declare integer GetWindowLong in user32 integer, integer
declare integer SetWindowLong in user32 integer, integer, integer

#define GWL_EXSTYLE       -20
#define WS_EX_TOOLWINDOW  0x80
#define WS_EX_APPWINDOW   0x40000

do form mytoplevelform name otemp noshow
local nhwnd,nstyle
nhwnd = otemp.HWND
nstyle = GetWindowLong(nhwnd,-20)
if bitand(nstyle,WS_EX_APPWINDOW) = WS_EX_APPWINDOW then
   SetWindowLong(nhwnd,-20,bitxor(nstyle,WS_EX_APPWINDOW))  && remove taskbar force style from Window
   nstyle = bitxor(nstyle,WS_EX_APPWINDOW)
endif
SetWindowLong(nhwnd,-20,bitor(nstyle,WS_EX_TOOLWINDOW))
otemp.Visible = .T.