IIS6.0 Application Pool
2 answers
In the IIS Manager MMC, you can see the node application pools and look in each application pool, or open the properties of each site and look at the application pool assigned to it.
There are also a few tricks available for managing application pools that I can dig out if that's what you're looking for.
You don't have to "browse" the sites to find out which is, unless I understand what you mean.
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