Hi Reddy.
1. At OS level you can refer the link http://www.windowsnetworking.com/articles-tutorials/windows-7/Configuring-Time-Windows-7-Win-2008-R2.html
2 Is it a new SAP system? When your are creating the new user id it will pop up the warning or error message about the time zone is not defined, Kindly refer the SAP Note point number 3 and SAP KBA
1375438 - Globalization Collection Note
2006897 - How to compare timezone settings between OS and application server with report TZCUSTHELP
Regards
SS