Kishore,
Are you trying to do this using Network Monitor or Web Prevent?
Network Monitor will only provide you an IP.
https://www-secure.symantec.com/connect/forums/lookup-get-user-information-http-incidents
Web Prevent will provide you a USER name but has the domain name as part of it.
https://www-secure.symantec.com/connect/forums/icap-and-winntdomainname
Please clarify..
Hope this makes sense.
If this solves your questions please marked as solved.
Ronak