Its all about IIS 7.5 .You must know

We got two important parts in IIS 7.5
Integrated Mode : I called it as Http Module Pipeline
Classic Mode       :       More of ISAPI

Further isolation:

User Mode: IIS Log
Kernel Mode : Refer HTTErr log..in windows/system32/LogFiles/..

One can use log parser to analyse the logs and find the root cause of the problem.

Important App Pool Settings:

1. Request Queue length Limit : Default 1000..
2. Overlap App pool recycle.
3. No of Worker processor.
4. Switch off Asp.net debug mode off..
5. Regular Interval of App Pool Recycle.

applicationHost.config file ( Found in location: C:\Windows\System32\inetsrv\config)

ApplicationHost.config is the root file of the configuration system when you are using IIS 7 and above. It includes definitions of all sites, applications, virtual directories and application pools, as well as global defaults for the web server settings (similar to machine.config and the root web.config for .NET Framework settings).

IIS Windows Process Activation Service (WAS)

Windows Process Activation Service (WAS) manages application pool configuration and the creation and lifetime of worker processes for HTTP and other protocols. The World Wide Web Publishing Service (W3SVC) and other services depend on WAS.

Name	Description
IIS Application Pool	An Internet Information Services (IIS) application pool is a grouping of URLs that is routed to one or more worker processes. Because application pools define a set of Web applications that share one or more worker processes, they provide a convenient way to administer a set of Web sites and applications and their corresponding worker processes. Process boundaries separate each worker process; therefore, a Web site or application in one application pool will not be affected by application problems in other application pools. Application pools significantly increase both the reliability and manageability of a Web infrastructure.
IIS Protocol Adapter	An Internet Information Services (IIS) protocol adapter is a Windows service that receives messages on a specific network protocol and communicates with The Windows Process Activation Service (WAS) to route incoming messages to the correct worker process. http://msdn.microsoft.com/en-us/library/ee377050.aspx