Sending keystrokes to a Directx Game (VC6)

Hi!
it's about 1 week that i'm trying to send keystrokes to a windowed 3d videogame.
It's a game where I'm able to chat or to use Keys to perform actions.
If chatting, (same window) i'm able to send keystrokes...if I'd want to eg:move my character, it just ignores the keystrokes I send
tried:

hwnd = FindWindow(vbNullString, windowname)
SetForegroundWindow (hwnd)
SendMessage hwnd, WM_KEYDOWN, VK_H, 0
SendKeys "h", True

and sendinput() too...
they all work for the chat only :(

how could it be?
I saw a Macro program with VBScript doing the job...how??
Any Idea??an example of code?
Perhaps .net ?