Network Admin Primer

Help. I am a programmer/PC support tech at a small company (120 users) and have been given the title of Network Administrator, with no training and big expectations.

I have been tasked with securing our network (16 servers), roughly 200 networked devices, about a dozen unamanaged switches, and 1 IT guy. Could anyone pass along some good links, articles, etc… for a Neophyte Network Admin?

I am mostly interested in how can I get information about my physical network such as traffic at each node, bandwidth usage, who is on my network and are they authorized.

I am doing my own research, but I figured why not ask the gurus.

Thanks,

David Stahlman