In many instances when your firewall blocks access to a remote system, or your spam filter traps a potential e-mail attack, the only information it reports about the source is an IP address.
To learn more about the individual or company behind the IP address, you can try using the command-line program nslookup in the TCP/IP networking protocol in Windows 2000 and XP.( You have to be connected to the internet).
To find the domain name associated with a cryptic IP address such as ‘126.96.36.199’ , click START, PROGRAMS, ACCESSORIES, COMMAND PROMPT. (Alternative way is to use the RUN COMMAND to open up the cmd window).
At the command prompt, enter nslookup followed by a space and the IP address. press
Type exit to close the command-prompt window.
For more findings, you can try www.iptools.com