connection problems

on ALOT of online games i have been having some lag/connection problems. on games like WarRock, Crysis and StarCraft i get alot of "cannot connect" or "cannot join" or im kicked cuz of lag. im connected directly into the DSL modem box (im pretty sure its the modem) and there are 2 other computers in the house that are connected through a wireless router (family computer is directly connected to the wireless router and brothers comp is connected wirelessly). would this be the cause of my online games lagging?? i also play maplestory and theres a delay when picking up items. picking up items should be instant but as u can see in this video

http://youtube.com/watch?v=yE2VnUIxA_8

if you actually play the game you can def see the delay, im pressing Z (pick up button) then ENTIRE time so everything should be picked up instantly. when the other 2 computers are being used the delay goes up to about 3-5 seconds. some1 told me it could be that my telephone wiring is old??? would that actually make a difference???