How does lua_touserdata work? Userdata also..

["phantom2023" <phantom2023@...>]

I have a function:


int l_Poke(lua_State* luaVM)
{
   char *address1 = NULL;
   DWORD address = 0;
   void *value = 0;
   int size = 0;

   address1 = (char *)lua_tostring(luaVM, 1);
   value = (void *)lua_touserdata(luaVM, 2);
   size = (int)lua_tonumber(luaVM, 3);

   if (value == NULL)
      MessageBox(NULL, "Uh oh", NULL, MB_OK);

   address = hextoint(address1);



   theScriptWindow->Poke(address, value, size);

   return 1;

}

called like:
Poke("0100579C", 5, 4)

in the script ( 5 being the value here)

It's supposed to be a void * because I want to cast it to BYTE, 
WORD, or DWORD depending on the size parameter.

However.. value always comes out NULL.

What am I doing wrong?