Listener Sam sent in this tip:
Spotlight is a wonderful wonderful thing, but some people have noticed occasions when a document or group of documents have not been captured during the indexing process. In such cases, one might want to reindex the volume. Apple did not build into Spotlight a way to reindex, but it can be done quite easily.
1. Open Terminal (in /Applications/Utilities/)
2. Type the following:
sudo mdutil -E /
to reindex the root volume, or:
sudo mdutil -E /Volumes/volumename
to reindex another volume named volumename.
3. Enter your admin password when prompted to do so and press enter.
4. You will receive the message “Volume index removed. Index will be rebuilt automatically.” in the Terminal window. You can monitor the reindexing progress in the Spotlight toolbar drop-down window.
5. Hooray, get back to using Tiger!