Whilst there are programs that can monitor the data usage, perhaps the easiest source of information is your current ISP. They do know how much you download.
When figuring your usage, remember you will use more when you convert to broadband. You can click a lot faster when the web pages appear almost instantly.
I did a quick search on ISPs available in your country (I'm across the Tasman), there are several companies that offer flat rate capped usage. This means that if you use more than you pay for, you will still be able to access the internet at a reduced speed. I notice that it is common for that speed to be 64kbs which is still faster than dialup. I'm currently locked into a plan which reduces my speed to 28kbs. Shared three ways that is really unusable. My little darlings have just blown out my monthly allowance in just ten days!
You will really apreciate the difference that broadband makes. Just make sure that you don't sign up on a plan where you do pay for excess megabytes. I recall reading about somebody in NZ allowing his daughter to use a file sharing program on broadband, that is until the $15,000 bill came in!
