I did a full installation of SQL Server 2008 Express. Looking at Add / Remove Programs, I see the following pertinent programs installed:
SQL Server 2008
SQL Server 2008 Browser
SQL Server 2008 Management Objects
SQL Server 2008 Native Client
SQL Server 2008 Setup Support File (English)
SQL Server Compact 3.5 SP1 Design Tools English
SQL Server Compact 3.5 English
SQL Server Database Publishing Wizard 1.3
SQL Server VSS Writer
SQL Server System CLR Types

And of course I also have installed .Net Framework 3.5 SP1.

I'm now trying to obtain sample SQL databases. To this end, and by the advice of others, I'm trying to install SQL2008.AdventureWorks_All_Databases.x86.msi. But whether I try to install "Sample Files" or "Create AdventureWorks DBs", I keep getting the following error:

PrepInstance() failed for MSSQL$SQLEXPRESS.
The following features are missing: Full Text Search

Running services.msc shows the following local services (but not SQL Server FullText Search):
SQL Active Directory Helper Service
SQL Server (SQLEXPRESS)
SQL Server Agent (SQLEXPRESS)
SQL Server Browser
SQL Server VSS Writer

Does anyone know how I can obtain the FullText Search service for SQL Server 2008 Express?

You really didn't need to create a new thread since this still relates to your previous one.