Accounting

I am in the process of setting up a GNU/Linux box for about a dozen
users in a hostel, each of whom will be allowed to use the computer
for a certain length of time.

Are there any tools besides ac that could help me accomplish that?

The idea is that users that have used up all their time would be
logged out and their accounts locked until an admin gives his ok in
some way. Basically it's the kind of setup an Internet cafe would
need.

I am to use SuSE Linux 9.1, most probably.

Any ideas?