Here is a related post in retrieving the site Id.
Here some code that might work for you:
using System.DirectoryServices;
using System;
public class IISAdmin
{
public static void GetWebsiteID(string websiteName)
{
DirectoryEntry w3svc = new DirectoryEntry("IIS://localhost/w3svc");
foreach(DirectoryEntry de in w3svc.Children)
{
if(de.SchemaClassName == "IIsWebServer" && de.Properties["ServerComment"][0].ToString() == websiteName)
{
Console.Write(de.Name);
}
}
}
public static void Main()
{
GetWebsiteID("Default Web Site");
}
}
Here's the link to the original post.
I'm not sure if it will work on IIS7, but if you install the IIS6 compatibility components for IIS7 it should work.