You just noticed a high CPU usage on your machine and the only indication from performance monitor (perfmon) is the process id and name (w3wp). It doesn't tell you which web site on your IIS is using the CPU. Here's how to get the info on IIS 7.0 using the Appcmd located at C:\Windows\System32\Inetsrv\ folder.
> Appcmd list wp 1288
The appcmd will print out the name of the Application Pool associated with pid 1288:
WP "1288" (applicationPool:Classic .NET AppPool - 80)
You can list all the Application Pools if you don't specify the process id.
> Appcmd list wp
This will show all the pools running and their process ids.
WP "1288" (applicationPool:Classic .NET AppPool - 80)
WP "2510" (applicationPool:SharePoint Administration v3)