Can two gamer tags play on xboxlive on the same 360 and tv at the same time?

Ok, weve seen conflicting answers to this and we are wondering. Me and my brother are planning on buying a 360 and getting Halo, Bioshock, and Gears of War. We were wondering though if we need to get seperate gamer tags so that we can both play our friends online at the same time... like isnt there a split screen option....and if we do decide to buy seperate gold accounts can we stil do that... thanks in advanced - JoeyCan two gamer tags play on xboxlive on the same 360 and tv at the same time?Well, you should. But, even if you can't you could just play and switch off talking.