Small business network monitoring

Small business network monitoring

Hi!

I would like help on being able to monitor my small business network. We have 10 computers on one router set up on the same network. I would like to know when each of the users on the 10 computers logged on and off, how much time they used their accounts.

I am not interested in what programs or internet sites they visited, just basic user account info.

Any ideas on free software (or Windows XP built in tools) that can help?

Thanx,