I selected the answer "run GUI from original CD...." Because from the following KB (http://msdn2.microsoft.com/en-us/library/ms144259.aspx#rebuilddatabase) it says:

To rebuild system databases for a default instance of SQL Server 2005 from the command prompt

1. Insert the SQL Server 2005 installation media into the disk drive.

2. Use the following syntax:

start /wait

None of the other options said to use the installation media.