Internet traffic limiter

I just need a small software or application that can be installed on a windows xp pro, this application would be able to count the incoming and outgoing traffic on my laptop, to avoid crossing the limit allowed. I need this application because the wifi that i connect to had limited the maximum daily usage of internet trafic for users and made it 512 megabyte per day, if this limit is crossed once my wifi account would be blocked for a week, so i need some control here.
Anyone can suggest a software that he tried himelsef?
thank you…