I don't need to do this very often, only when I install a new IP-based device that has static IP address assigned by manufactory but lacks of documentation.
I recently purchased an APC Environment Management Unit due to the temperature issue I am having in our server room. The device looks awesome but I was having the problem finding its IP address. It was mentioned on the quick installation guide that it uses DHCP to get the IP address automatically if there is an available DHCP server on the network but I saw no records related to this new device on the DHCP server assigned addresses pool at all. I was stuck because I only know its MAC address and there is no way for me to find it out without a proper tool handy.
Then my assistant came over and mentioned a shareware tool called CC Get Mac Address which is designed to find MAC address and computer name from IP address. So I downloaded and installed on my Vista. And did a quick scan and magically found out the IP address associated with the MAC address that matches the APC unit. Hula...it turned out that the APC unit has its default IP address 192.168.0.100 assigned by manufactory. And this IP address falls into my DHCP IP address pool.
I believe there are probably a lot tools like this CC Get Mac Address out there on Internet and some of them even comes free. So it would be handy to at least know where to look when situation like this happens.