In both MOSS and Search Server it is possible to configure an xml file that controls expansion and replacement words, so in effect this is a thesaurus file that you can customise with words that may be specific to your organisation.
The classic example given is one which expands the technology acronyms (computer types sure do like them!):
1: <XML ID="Microsoft Search Thesaurus">
2: <thesaurus xmlns="x-schema:tsSchema.xml">
3: <diacritics_sensitive>0</diacritics_sensitive>
4: <expansion>
5: <sub>Internet Explorer</sub>
6: <sub>IE</sub>
7: <sub>IE5</sub>
8: </expansion>
9: <replacement>
10: <pat>NT5</pat>
11: <pat>W2K</pat>
12: <sub>Windows 2000</sub>
13: </replacement>
14: </thesaurus>
To find the location of this file you first need to look in the registry under: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0\Search\Global\Gathering Manager] Key: DefaultApplicationsPath
Once you have found the file you can simply add expansion and replacement elements with the children nodes as needed.
Don’t forget to do this to all the servers in your farm. Also you will need to restart the search service for these changes to take effect.
The following table (from the enterprise search blog) lists the elements and what they do:
I’ve only scratched the surface here, for a full overview of this topic, check out the enterprise search blog
Don’t forget that SQL Server full text search (FTS) has the same capabilities in terms of a thesaurus file that supports expansion and replacement words. If your looking for information on SQL Server 2005 or 2008 you should refer to this post.
The other feature that both products support is the notion of noise words, these are words that when used add no value to the search like ‘been’, ‘before’, ‘being’, ‘both’ etc. This KB describes the process to add or remove words from this list, but simply it is modifying the contents of a file which lives in: Data\Ftdata\SharePointPortalServer\Config, it’s a simple format where each word is on it’s own line (no xml).
Have fun customising the search experience.