Please help my administrator got canned!

My administrator was fired today on some pretty bad terms and it seems that im in charge of everything for a little while. I have a decent understanding of the current system but I really need some help where to start. We currently have a network of80 Win 98 nodes connected to a NT Server which also emulate from a unix box. We are running an exchange mail server and have some sought of linux firewall set up. We all access the net through a dsl line. Im 22 years old and Im really not prepared for this shit. Could someone please give me some sought of checklist or some place to start. God save us all. Help!!#?@! chesire1@aol.com