wireless internet problems

my internet is ran through a wireless router from my mums which is the main internet terminal, when we both had pc's this worked fine but since i have bought the mac it has been majorly playing up and only letting 1 of us on at a time, and when we atempt 2 one of us will be thrown off within 2 mins.

any ideas?

our provider is ntl and the wireless router is actiontec

also when i visit sites like facebook or myspace my computer kicks me off the internet, anyone have any answers for this?

thanks.