I'd like to search for a given MAC address on my network, all from within a Python script.  I already have a map of all the active IP addresses in the network but I cannot figure out how to glean the MAC address.  Any ideas?
Depends on your platform. If you're using *nix, you can use the 'arp' command to look up the mac address for a given IP (assuming IPv4) address. If that doesn't work, you could ping the address and then look, or if you have access to the raw network (using BPF or some other mechanism), you could send your own ARP packets (but that is probably overkill).
Search for host with MAC-address using Python