Don't confuse indexes, source groups, search scopes  and content  sources.
Search scopes are built  off of source groups, not index  files or content
sources.

Here's the most granular way to do this, without having to worry about
index files.

1. Create four content sources  - two of them will be for the sites
directory and two for the sites  direction areas  (one each).

2. Place the two content sources (one for the site  area and the other
for the sites directory) in the same source group. Do the same for the
other two, but in a different source group.

3. Build your search  scopes and away you go.

Now, the gotcha here is something that I just learned today: the sites
directory content source does *not* crawl the sites directory area  in a
portal. Instead, it crawls the sites that are listed in the Manage
Sites to Crawl page. It is the portal  content source that crawls the
sites listed in the Sites Directory.

I was *stunned* today. But I tested it and I'm 90% sure I'm right on
this point. I'll post something to my blog soon about this. So, in
effect, if you want the Sites Directory content source to crawl all of
the sites, then they need to be listed in the Manage Sites to Crawl
page. By default, embedded sites are added to this page, but if they
are not, then they are not crawled by the Sites Directory content
source.

Help me understand - this is what I did, but I'm not quite getting the
results I would expect. The first search  scope is Corporate Events, and
the second one is Accounting. We'll just use Corporate Events as the
example, because I assume the steps are all the same for Accounting.

1) Go to site  Settings >> Configure Search and Indexing
2) Add content  Source
3) For the first content source, I selected the following settings:

- Non_Portal_Content Index,
- SharePoint portal  Site Directory option
-
http://servername/C2/Corporate%20Events/Lists/Sites/Summary.aspx for the
address (this is the sites  portal area  for Corporate Events).
- Description: Corporate Events Sites
- Adaptive Updates checked
- Source Group - I manually entered "Corporate Events Sites"

4) For the second content source, I selected the following settings:
- Portal_Content index  (I was guessing here)
- Web Page or Web Site option (I was guessing here too)
-
http://servername/C2/Corporate%20Events/Lists/Sites/Summary.aspx for the
address
- Description: Corporate Events Sites
- Crawl Configuration: This Site - Follow links...
- Participate in Adaptive Updates
- Source Group - I selected Corporate Events Sites

5) Returned to Site Settings >> Configure Search and Indexing
6) Manage Search Scopes >> New Search Scope, and used the following
settings

- Name: Corporate Events
- Topics and Areas: Limit to the following Areas: Corporate
Events
- Content Source Groups: Limit to: Corporate Events Sites
7) Reset both portal and non_portal content indexes, and start full
updates on both.

My search results yield only the Corporate Events area page, and not any
of the sub pages.