HTTP Status Code 503, App pool Out of resources.

Hi All,

I am running with sCOM 2007 R2 and we are monitoring couple of url's.  we got an issue with one of the  website is not

 accessible and we got an alert in SCOM from webapplication template. The HTTP Status code is 503.

I understood that 503 error code is for out of resources in AppPool.  correct me if i am wrong.

here is the requirement for me:

Need to monitor  these resources and need an alert before resouces fully utilized.

please suggest me how to configure these montors.

Thanks in advance.

John