With IIS creating w3wp.exe’s for all of your apps (for which you have created a non default app pool) it is nice, but it’s impossible to tell exactly which is which. Microsoft includes a handy tool to do this with it’s in: %systemroot%system32iisapp.vbs (You may need to run it with cscript.exe if that’s not your default for .vbs).
W3WP.exe PID: 2028 AppPoolId: DefaultAppPool
W3WP.exe PID: 20224 AppPoolId: Autotransactiondocs
W3WP.exe PID: 17480 AppPoolId: IRAppPool
Oh, this is for Windows Server 2003 (and r2) only.. does not work with 2008 variants.