I'm on a office network and there are around 12 PCs that are connected to a switch and then to a Prolink Router. Now the Internet connection is very slow and I'm the one who manage all the computers. I want to monitor bandwidth usage of each computer on the LAN. how can I achieve this using my computer. I cannot install any software on the client computers other than mine.

I tried wireshark but, it only shows my network usage so there is no use with the data I get from it. Is there any specific software that I can use within my PC to get the bandwidth details of other computers. I'm on a windows 7 x64bit PC with admin privileges.

Thank you.