Small Business Server 2000 Problems

I am working on a SBS 2K server that is having issues. When I log on locally to the server as administrator almost everything is very slow to respond. I can’t get the internet to open, browsing the hard drives is slow. But the processor utilization stays below 20%, Memory usage is low. If I send an email out it goes almost immediately and incoming mail takes about 30 minutes to go through the system. If I access the server through the network I can browse the drives with no problems. I am really looking for suggestions where to look next.

Thanks