RARP no mo. How do I find IPs from MACs?

Anybody got a quick & easy means of resolving MACs to either IP addresses or (better yet…) BIOS/network names? ARP goes one way (IP to MAC), and RARP isn’t available on the W2000 server where I was monitoring network traffic. I know there are probably a FEW methods that are plenty tedious, but I want something easy – OR RARP back!