I've been working with the Pogoplug recently, and realized that people may have difficulty locating a new device on their own network.
Most networked devices get an IP address dynamically, using DHCP. That is to say, the IP address of your net device could change on a regular basis. And you have no good way of knowing what it is.
Most of the time, this won't matter to you, but if you need to log in to a network device, you'll probably need to know the IP address.
To locate the IP address, first find the MAC hardware address. Just look at the bottom of your device, or on the label with your serial number. Usually, there will be a line for the MAC hardware address, or it may be known as the device hardware address.. This will be in the format of 16 characters, in 8 pairs, separated by a colon (":") or a dash. The characters will be 0-9 and a-f. Write this down.
Now, you'll need to look at your DHCP server and look at the client leases. One of the leases will have the MAC hardware address of your Pogoplug listed. That entry will probably not have a name, but it will have an IP address. For an IPv4 address, the address will look like 4 numbers separated by dots, like 192.168.1.101 or something similar.
For most users, the DHCP server will probably be your router. Usually, the DHCP leases are listed in a table in the "status" section of your router's web interface. If you are not sure, just do a Google search on "router-name dhcp table".
If you don't have easy access to the router's DHCP table, you can use a brute-force approach. Download an IP address scanner (I use the older version of Angry IP Scanner) and have it scan your local network. This will have the affect of populating your ARP table (which is a list of all known devices). In Angry IP, you can also display the MAC address. Look for an entry that matches your device.
To make sure it IS really your device, try to ping the IP address. (Yes, Google it if you don't know how.) Once you have managed to ping the IP address successfully, examine your ARP table for the MAC hardware address. The command to type is "arp -a". If you find a MAC address in the ARP table that matches up to your device, you should have the right IP address.