&H3 is the Visual Basic way of displaying a hex value. &H3 is the equivalent of 0x3.
To get the hiword and lowords from a number use these
js code:
/*
Name: lobyte
Purpose: Retrieves the lobyte from a value
Parameters: w - the value to get the lobyte from
Return: lobyte of the w parameter
*/
function lobyte(w){ return w & 0xff; }
/*
Name: hibyte
Purpose: Retrieves the hibyte from a value
Parameters: w - the value to get the hibyte from
Return: hibyte of the w parameter
*/
function hibyte(w){ return w >> 8; }
/*
Name: makeword
Purpose: Creates a WORD value by concatenating the specified values.
Parameters: a - Specifies the low-order byte of the new value.
b - Specifies the high-order byte of the new value.
Return: The return value is a WORD value.
*/
function makeword(a,b){ return a | (b << 8); }
And for your last question you would do something like this
js code:
function OnWindowEvent_MessageNotification(pPlusWnd, nMessage, wParam, lParam){
switch(nMessage){
case WM_MOVE:
/*
your code here
*/
}
}
/ 
