Computer Overuse

Question:

Dear Jane or Associate:
I attended your seminar in Portland on May 15 and enjoyed listening to your suggestions. It is always good to be reminded that respect is the foundation for any good relationship. Thank you for your work! I do, however, have a question that I’m still not sure how to deal with. Here goes:

We have 3 daughters, ages 13, 11, and 7. The older two really like the use of our computer, especially e-mail and instant messenger. As a family (at one of our weekly family meetings), we agreed on what the rules pertaining to the computer would be. They are things like:
Homework and chores need to be done first 30 minute time limit (not including homework use)
Safety issues, etc.

We concluded that if these rules were not adhered to there would be a consequence, namely losing the use of the computer for the next day. We have done that, yet it seems that the rules continue to be broken and that I spend too much of my time monitoring, reminding, and revoking the use of the computer. Is there a more positive, less “parent as the enforcer” way to handle this situation?