Here are two functions I wrote a while back. The first one returns the app bar height, the second one checks if the bar's auto hide feature is active:
function GetAppBarHeight()
local hap
local result
Load Dll "user32.dll", 1
hap = Call Dll(1, "FindWindowA", "Shell_TrayWnd", "")
if hap = 0 then ExitFunction 0
make memblock 1, 16
Call Dll 1, "GetWindowRect", hap, Get Memblock ptr(1)
result = Memblock Dword(1, 12)- MemBlock Dword(1, 4)
delete dll 1
delete memblock 1
endfunction result
function AppBarAutoHide()
local result
Load Dll "shell32.dll", 1
make memblock 1, 36
write memblock dword 1, 0, 36
result = Call Dll(1, "SHAppBarMessage", 4, Get Memblock Ptr(1))
result = result and 1
delete dll 1
delete memblock 1
endfunction result