I need a software to limit internet access time

[Voroojack]

Hello,
I'm an administrator of a company with about 150 computers, which their users must access the Internet. But the company has decided to limit its users from accessing the Internet more than a specified time in a day. I'm looking for a good monitoring system which can work with Active Directory that means I want it can get its users and give me the ability of defining time limits for each user, does anybody know a software to do this?
Thanks a lot! :)

[YeOldeStonecat]

Microsoft I.S.A.

[kletool]

We´re using Surfcontrol Webfilter since 2002. Perfect Solution. - Catagory´s updated hourly. - Categories Chat, Streming Media (youtube, etc.) are set to 1/2h per day. Download of exe´s and other unsafe staff forbidden.
Since Surfcontrol was bought from websense last year i´m not shure, if the product is still available.