To find the IP address of the VPOP3 computer, in Windows go to Control Panel → Network and Sharing Center.
Press the Local Area Connection link
Then press 'Details'.
Look for the 'IPv4 Address' setting.
The above instructions are for Windows 7, earlier versions of Windows may vary
One way which works in all versions of Windows is to open up a Command Prompt and type 'ipconfig' Under the heading 'Ethernet Adapter Local Area Connection' look for the 'IPv4 Address' line.