what kind of video card are you using?
what kind of network card are you using?
and what Operating System are you running?
do you have 1 network card in or two? disabling the unused one may help, no need to take up IRQ's.
Try updating your Operating System, are you using an old OS?
Maybe its your router/modem. you said your laptop runs fine, is your laptop plugged into a different port, try connecitng the ethernet cord into another port.
TRY EVERY PORT!
and i guess the last thing would be to ask who is your Internet Provider?
Ive never had this problem but even when i had a 500 ping....i didnt have spikes, it was just all high...and my game ran fine, it would be the weapon response that was slow (lagged)