Network Monitoring Program more simple than "MS Network Monitor v3"?

Hi, i have been appointed the "sysadmin" of my small organization's
network (since i supposedly know more than anyone else here,
debatable) and my first task is to find the bandwidth hogs and IM
slackers.

We have a linksys router and everyone insists on using windows so it
is more or less a windows network. We do not have a server (yet, i am
lobbying the director but its an uphill battle) so i don't have a
computer where all the traffic goes through. I found MS Network
Monitor v3.x (http://support.microsoft.com/kb/933741) and it *seems*
to do what i need like view network traffic w/o being installed on a
server only problem is that it is waaaay over my head and i have
little concept of how to filter/interpret the data.

I am trying to find a free app (lobbying my boss for a server is hard
enough as is w/o investing in even more software) that will simply
allow me to identify the sites users are visiting, how much they are
down/uploading, what they are down/uploading, and the services they
are using and how often they are using them (mainly instant
messaging), etc etc etc. And of course the information needs to be
understandable by someone like me (ie "advanced user" but not hacker/
sysadmin/guru).

Any help or suggestions would really be appreciated!

Cheers

-Gaiko

gaikokujinkyofusho@gmail.com