win32-process.rb

require 'win32/process'

process_info = Process.create(
    :app_name         => "notepad.exe",
    :creation_flags   => Process::DETACHED_PROCESS,
    :process_inherit  => false
)

win32api.rb

close_handle = Win32API.new('kernel32', 'CloseHandle', 'L', 'L')
create_process = Win32API.new('kernel32', 'CreateProcess', 'PPPPLLLPPP', 'L')
startup_info   = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0].pack('LLLLLLLLLLLLSSLLLL')
process_info   = [0,0,0,0].pack('LLLL')

created = create_process.call(
    0,                  # lpApplicationName
    "notepad.exe",      # lpCommandLine
    0,                  # lpProcessAttributes
    0,                  # lpThreadAttributes
    0,                  # bInheritHandles
    0x08,               # dwCreationFlags
    0,                  # lpEnvironment
    "C:/Temp/",         # lpCurrentDirectory
    startup_info,       # lpStartupInfo
    process_info        # lpProcessInformation
)

close_handle.call(process_info[0,4].unpack('L').first)
close_handle.call(process_info[4,4].unpack('L').first)