Need help with service to limit printer use.

Question

Greetings,
I am a web developer trying to create a windows service to limit the number of pages a user can print each day. I was thinking I'd save the total in isolated storage. What I would like to have happen is if the limit has been reached a dialog box would inform the user that the daily limit has been reached and not allow them to print.
I know how to create a windows service and a little of COM+/WinAPI but I need to know what windows message that coresponds to the print dialog opening. 
I could not find anything on the web. Could somebody send me some links that might help?