Computer keeps disconnecting from the internet

I just got BT Infinity and whenever I download something or run speed test (speedtest.com) my computer disconnects from the internet and shortly after connects again. How do i fix this?
I am running a dell latitude d600 with windows xp. Before bt infinity i just had a normal bt home hub and that worked fine. I don't think this is happening on other computers connected to the network but i can't be sure. I am using Wi-Fi, not ethernet and i haven't tried connecting via ethernet yet but the hub is in a different room and i cant move anything from room to room because of the set up.

A previous answer i got was to re intall my wireless router. I thought this had worked, but it only suspended the time before the disconnect for about 1 min. Then it just went back to disconnecting straight away again.