Recently, my OS X Leopard system ceased showing to me all the important files on my external hard drive in a spotlight search. A general Spotlight reset did not help, as it only reindexed the system hard drive.
Luckily, you can manually rebuild the index via terminal:
sudo mdutil -E /Volumes/[Drive Name]
Here is links to the Apple manual pages for
mdutil and mdimport
By mdimport you can manually add information on new files and directories to your Spotlight index.