W3Wp.exe belongs to which AppPoolID ?

If you have different application pools and you need to know which application pool  the worker process belongs to, run the following command.
C:\WINDOWS\system32>cscript iisapp.vbs

AppPool recycle

Instead of restarting the IIS using IISReset, which would recycle all the AppPools on the server, you can just recycle the required AppPool using the following command:

%windir%\system32\cscript.exe c:\windows\system32\iisapp.vbs /a "[App Pool Name]" /r

You can create a shortcut for the above and add it to your toolbar

How to determine the Password for IUSR account

Click on the Image to get a better view
Below are the commands for accessing the password's for the respective accounts

src link: http://support.microsoft.com/default.aspx?scid=kb;en-us;297989