Keep track of those damn IPS

Hello out there,

We manage multiple small business offices, for multiple companies. Our standard setup is an SBS acting as a Domain Controller and all the machines joined to the domain, so anyone can log in anywhere.

Each company is allocated a subnet range, as in 192.168.18.0/24 and then we would have GRE tunnels to all the offices, allowing us to access those ip's from our office.

The problem is that every computer and phone is using DHCP, so unless you go directly to the company's SBS, it is quite hard to track down all the ip' s and monitor them. Optionally log in to the router, and look up through the arp table.

Some of the client' s networks are running OSX server and mac clients.

What I was wondering is that if any of you guys knows an app, to be installed either on the SBS's or the client machines, or a way, that would allow me to have a centralized list with all the ip's currently in use and a description, for example the machine name, or ID, or anything.

I have managed to create a list using fping, but obviously, that only tells me the IP and nothing else.

Any ideas, helps or tips would be greatly appreciated.