If you want to see how much data you've used in your current internet session go to Start > Control Panel > Network Connections. You should see an icon showing your phone/3g modem model, double click the icon. A new window will pop up showing current speed, data sent, data received etc. If you are using xp when you're online there should be two little computer monitors next to the time on the taskbar, put the cursor over that and a balloon showing speed, data sent and received will pop up.