JeannieM 0 Newbie Poster

This is for my grandson who has a wireless modem for internet connection and has a Mac laptop, a pc with 100g hardrive and have an xbox 360
we have plugged in a wireless network adaptor on the xbox so to play online
my problem is when he is playing live on the xbox the internet connection keeps cutting out and vice versa when someone gets on my pc or Mac the xbox disconnects
It seems to be that they are both fighting for internet connection and can't find it
I would think that if it is a wireless modem it should pick up all computers and keep everything on at the same time
thanks