VBScript and Windows Script Host don't provide intrinsic functions for maximizing/minimizing/restoring a window. Without any third-party tools, your only option is to use SendKeys
to simulate keyboard the shortcuts of the corresponding commands in a window's system menu.
To maximixe the active window, you can simulate the Alt+ , x shortcut:
Set oShell = CreateObject("WScript.Shell")
oShell.SendKeys "% x"
To minimize the active window, use Alt+ , n:
Set oShell = CreateObject("WScript.Shell")
oShell.SendKeys "% n"
To restore the active window, use Alt+ , r:
Set oShell = CreateObject("WScript.Shell")
oShell.SendKeys "% x"
(Note that this code won't work in non-English Windows versions, where the names of the Maximize/Minimize/Restore commands are localized and therefore have other shortcuts.)