* Viacom said tens of thousands of videos posted illegally * Google, YouTube said protected under copyright law * Viacom sought $1 billion in lawsuit, plans appeal (Adds details on ruling, complaint, other companies) NEW YORK, June 23 (Reuters) - Google Inc GOOG.O won a landmark victory over media companies as a Manhattan federal judge threw out Viacom Inc's VIAb.N $1 billion lawsuit accusing the