you can send to all html windows, you just need to change the viewtype, but but the name of npcs window is "NPCDialogWnd".
the function for you to understand how to send to another window:
function HandleLoadHtmlFromString(string param)
{
local string htmlString;
local int tmp;
ParseString(param, "HTMLString", htmlString);
ParseInt(param, "isExtra", tmp);
if(tmp != 1)
{
m_hHtmlViewer.LoadHtmlFromString(htmlString);
ShowNPCDialogWnd();
}else
{
m_ScriptExtra.HandleShowBoardPacket(param);
}
}