in the new game fallout 3 for the xbox 360 will there be any online co-op and if there is how many people can u play with

No.
It is a single player online game, and they didn't put in because the developer wants everything perfect and on-time, and they feel co-op would be rushed. Also the game is fine without co-op. Get it anyway, Fallout 1 and 2 were some of the best games ever.

you can play with 800 people at the same time. jk. simgle player only