MacBook has a very slow internet connection.

I got a macbook pro two days back. It worked fine with my Beetel 450TC1 router for a night. I was able to download the OS update in half an hour. Sice then, the connection has been painfully slow- around 34 kbps. Other computers in my home network work fine. They were able to achieve a download speed of upto 2 mbps. However, when I connect my macbook to the network- either by ethernet or by wifi, they too start experiencing similar problems. I initially figured the problem must be with my Internet Service Provider, Airtel, and approached them. They gave up after changing the router a couple of times. I then tried the local istore. But the internet- wireless, worked perfectly well there. Probably because they have an airport extreme- I don't know.

Is it probably because of the OS update, which incidentally also included an airport update? I'm trying to figure this out. What do you guys suggest I try next?