How to monitor the activity of a PC LAN network?

[BenTen]

Work would need to track different PC connected to a LAN network through a router is connected to a server used for business purposes to which I can not install anything.
what I want to know more and are used as a PC, what programs are used more frequently and "especially" to know which of them is dealing with more bandwidth, because, because of some Hacker initiating a p2p program that we often the whole network slow down at times with the inability to work and drop the connection if the server is trouble ....

I've tried look LAN monitor, but the same can not give me the information I need more, that is, which employs more PC band and what program to use more ....

know something suitable for this purpose, possibly free, open to install on a machine with XP where to control everything ...?

[Learning One]

Ben
I use a program call spiceworks. It is free and will tell you a lot about what is on your network. You can run it from your desk top. They add improvements all the time so it gets better and better all the time.

[Milton.J]

Ben
I use a program call spiceworks. It is free and will tell you a lot about what is on your network. You can run it from your desk top. They add improvements all the time so it gets better and better all the time.

Yes, Spiceworks combines everything you need to manage IT in one easy-to-use application:

• Software inventory, network inventory, PC inventory. Inventory every IT thing you manage.
  
  
• Network monitoring, Exchange monitoring, license monitoring and more. Stay alert!
  
  
• Asset reporting, inventory reporting... share a report. Report to your heart's content!
  
  
• Helpdesk & IT Portal. Let 'em submit a ticket! Now you can track every IT task and project.