Loss of drive space on boot drive

I have an NT 4.0 sp6 server that keeps running out of drive space. On the boot drive the OS and Norton Antivirus loaded. It started as a 2g partition and I am now almost out of drive space. Is there anyone who can tell me what to look for? Is there a tool that can watch file and directory sizes? This server is the PDC and has DHCP running on it. It also has the network printers setup on it. When I reboot it doesnt gain any space. I have run diskeeper on it also and that didnt help.