SInce safari update internet connection virtually non-existent

Hello! I wonder if anyone can please help. I own a mac air (2011), running snow leopard. My computer, which I otherwise love, is driving me crazy with it's internet connection - it's running incredibly slowly and / or times out. I think it's related to the auto safari update from a couple of weeks ago (which if I remember had something to do with Lion) but it's also a problem when I try running chrome now.

My boyfriend has a macbook and there isn't a problem with his connection at home (it's running speedily).

I've tried the DNS 4.2.2.1 thingy but it hasn't helped.

Can anyone offer any advice? It's becoming incredibly annoying! (I would need 'baby steps' advice, if folk could be so patient as to provide that).

Many thanks!