As JavaFan said you would need to clarify what you define by internet usage, and there is unlikely to be a module on CPAN that will work out of the box.

For myself, I wrote a script a while back that connects to my broadband router, and reads the cumulative packets sent & received page. It reads the numbers once a minute, and puts them into either a CSV file or a database. From there I can import the numbers into a spreadsheet or whatever and analyze it for cumulative usage, usage at various times of day, or anything else I am interested in.

It should not be to hard to do the same, and I know of at least one windows shareware program that does that. If you would like a copy of the perl script I wrote then let me know. (It runs on Linux and talks to a Netgear router).