solve lagging problem on my network with QOS
i got a network of 20 computers. Using ADSL from starhub. When some of the computers are downloading stuff or watching youtube, gaming will lag. to solve this problem, i bought DIR-655 Xtreme N Gigabit Router http://www.dlink.com/products/?sec=0&pid=530 and connnected in this fashion :
starhub modem ==> dlink router ==> hub ==> 20 computers
in my QOS, set maple story as priority 1 ( highest) as shown here

unforturnately , when downloading at high speeds, other computers playnig maplestory will lag. ping to yahoo.com is about 1000ms. does anyone know how to solve this problem?
experts please help