File where your XP accounts and passwords are stored

In windows xp,when ever we login,we have to provide a userid and password.The system will then try to match this parameter from a file where it has stored account info.So which is that file is the main Question?
c:\windows\system32\config\ SAM
Yes,SAM file contains the information.But we cannot copy and export or delete that file,it will show you the file is being accessed by some other process.System process is running behind the screen and it doesnot allows you to copy,delete or modify.
Even you cannot kill the system process,if u try to do ,you will get a system shutdown message with in a minute.and your system will be shutdown within 1 min(type shutdown -a in dos prompt to abort shutdown)

So can we know the password of the user.Yes we can use a tool called SAM Inside which can use BruteForce and Dictionary attack to get the password for us.
Dont try to copy SAM from Dos safe mode.still it will show you same message.

Good Luck