Question:
Is it possible to use API to determine the OS of a system without resorting to SysInfo control?

Answer:
Sure. Just call the GetVersionEx API. Add the following to your Declarations section:

Private Declare Function GetVersionEx Lib "kernel32" _   Alias "GetVersionExA" (lpVersionInformation _   As OSVERSIONINFO) As LongPrivate Type OSVERSIONINFO   dwOSVersionInfoSize As Long   dwMajorVersion As Long   dwMinorVersion As Long   dwBuildNumber As Long   dwPlatformId As Long   szCSDVersion As String * 128End TypePrivate Const VER_PLATFORM_WIN32s = 0Private Const VER_PLATFORM_WIN32_WINDOWS = 1Private Const VER_PLATFORM_WIN32_NT = 2

Then, to make the call, declare an instance of the OSVERSIONINFO type, fill out its length member, and pass it to GetWindowEx:

   Dim os As OSVERSIONINFO   os.dwOSVersionInfoSize = Len(os)   Call GetVersionEx(os)