Very useful info I found at Simple-Talk and don't want to lose. Go there for the full article on SQL Server Full Text Search: Language Features
The iFilter used depends on the data type of the column in which the data is stored and on how you have configured your full-text index:
For columns of the CHAR, NCHAR, VARCHAR, NVARCHAR, TEXT, and NTEXT data types the indexing engine applies the text iFilter. You can't override this iFilter.
For the columns of the XML data type the indexing engine applies the XML iFilter. You can't override the use of this iFilter.
For columns of the IMAGE, and VARBINARY data type, the indexing engine applies the iFilter that corresponds to the document extension this document would have if stored in the file system (i.e. for a Word document, this extension would be doc, for an Excel Spreadsheet this would be xls). Please refer to the later section on Indexing BLOBs for more information on this.
NOTE: It is important to understand that an iFilter can launch a different language word breaker from the one specified as the default in the full-text language setting for your Server, or from the word breaker you set for the column in the table you are full-text indexing. I cover this in more detail in the Word Breaker section.
A complete list of built-in iFilters is accessible from: http://www.indexserverfaq.com/sql2005iFilters.htm. You can also obtain a list of the signed iFilters that are currently accessible on your SQL Server 2005 by issuing the following query in any database:
select document_type, path from sys.fulltext_document_types
The iFilters are listed in the path and the document types that are indexed by the iFilters are listed in the document_type column. Note that although there are iFilters for asp and aspx pages, these pages will not be generated by the asp or aspx rendering engines, rather the HTML MetaTags and textual content between the body tags will be indexed and searchable.