Apple Thoughts: What's On Your Network?

"Adding TCP/IP devices to your network is, for the most part, a pretty straightforward process. If you are using DHCP, just plug the device in, and it will grab the next available address. In some cases, you may want to manually set an IP address, but this shouldn't be an issue for small networks. However, if you are on a larger network, or there are devices that aren't under your control, you may start running into issues. Fortunately, IP Scanner can help."

If you aren't sure you need something like this, you can get the free version first and try it out. With the free version it will only give you info on the first six devices it finds, but it is the same detailed information from the paid version, which is $29.95 USD. You can check it out at 10Base-T Interactive.