I have spoken to him on msn and have pretty much cleared all the basics. No router hacking to steal password, no p2p, no kids downloading and no wireless.
One thing that seems strange is that it's uploading that's higher. Main cause for high outgoing is p2p > people downloading from you, uploading things to sites like websites, big files or pictures, sending large amounts of emails or lastly a virus sending itself all over the place via email or some other means. One other thing mentioned above is that it could be an inside job.
Like the idea of getting a bandwidth monitor. You could also check at the bottom right of the screen in the task bar. There should be 2 screens that come on everytime you dial a connection. Right click on the internet one and click status. Under activity you can see what you have sent and recieved as well as the amount of time the connection has been active. I would suggest that after a normal session of surfing to check the amount of usage as well as the time to see if they corrospond with 2 gigs in 5 days.
So if there is nothing that you find that explains the high usage then I'de suggest getting a prepaid 1 gb account from
http://www.webafrica.co.za to see if the usage is still so high. If it's lower then you know something is going on. Then atleast you can figure out if it's from your side or from the ISP.