well if you are on wireless and are nat 2 i'm assuming you already have DMZ and port forwarding options set.
buy a nicer router, one that has an N rating. Make sure your the only one on your wireless network. I don't use a password on my router b/c WPA2 encryption will not let me ever be nat 2. So I have to hide my broadcast signal and set my router to only accept the MAC addresses I tell it to.
I have 1.5 mb cable here in the USA and it lags all the time. I thought it was just my router, but even through speed tests on the pc it would lag and flucuate.
This happens especially at night time. I go from streaming netflix in x-high def down to low sd, drops in and out. Last night for example I couldn't get anything higher than high sd.
either get something insane like 50 mbps , or just try to play earlier in the day if the other options don't work for you