This older article from Macworld (April 3, 2008) discusses Spotlight searching for Tiger (Mac OS 10.4), but it is still relevant now for Leopard (10.5). The major benefit in 10.5’s spotlight is the speed improvements, and some changes in the search results window(s)….

On the surface, searching with Spotlight is pretty straightforward. In our previous installment, we covered the basics of using and customizing the Spotlight menu. But if your search involves multiple terms, or if you need to narrow down your results to dig up a particularly elusive file, knowing how to put together a good search query will pay off. By mastering a few simple tricks, you can limit your search to specific types of data, exclude terms, and more—helping Spotlight locate exactly what you need. and then take you inside some of its lesser know features—including how to use keywords to limit your search to specific dates, authors, or file types.”

See Create good queries in Spotlight | Software | Macworld for the complete article.