Actually this is my first installtion or upgrade on server machine so could any one help me with good document how to upgrade the systems from moss 2007 sp1 to sp2 so is there any nice document which clearly explains the preventive measures to be taken, pre-requisities to be checked,installation process and which how to check if that instllation is done sucessfully. Could anyone let me with this information.

Read this http://technet.microsoft.com/en-us/library/cc263467(office.12).aspx From my expirience I suggest you make full SharePoint backup before start the upgrade.Oleg