Lag+gaming question

My fastest and best connection I've personally owned so far is 28 k. Not 56 k. At least with 28 k dial up I knew what I could and could not do. Then I got hughes satellite. It sucked for playing real time games.
Now I have cox high speed and I'm having troubles.
Heres the situation.

My computer is in my room. The host computer is in the room next to mine. I'm a guest to a network so I could get access to the internet. I'm using a netgear wireless router. Now day 1 everything is running fine then at about 1230 when everyone's asleep I'm the only one up playing a video game. I get these lag spikes that make gaming unplayable.

Now there's another computer in the living room hooked up to the same network and lag spikes are frequent. There's more time of laggy game play than there is of normal well connected game play.

Anyway I was hoping someone might have some tips as to what I can do to fix this problem. I understand that I might have to answer some questions. And that's fine I'll be checking this thread often for the next couple of days.
Lag spikes seem to be randomly occurring sometimes when all three computers are running sometimes when I'm the only one online.

Try using ethernet cable one time when the lag spikes usually occur, see if this resolves it. If it does at least you have isolated it to the wireless.