dtSearch is a powerful search engine. You can control indexing and searching with COM objects very easily. And you can index whatever you want with a mean called "DatasourceToIndex". BUT, samples for this way of indexing are only available in VB... and I'm developping with Delphi.
I had many difficulties to find samples, even to write this damn' IDispatch object in Delphi. It's the reason why I publish this source code... It contains the good declarations and even the way to index files adding some extra fields for each file.
The source for Delphi 7, with the binary (~260ko) :
dtSearch tips 
dtSearch Engine, IIndexJob and DatasourceToIndex property