Did you know that you can view an item's enclosing folder (and all of its content) directly in Spotlight (a Mac OS X 10.4 Tiger feature)? Just Command-click the item in the Spotlight search results window to view it in a Finder window!
Here's another way: Click Show All in the Spotlight search results list, select the item of interest in the resulting window, then press Command-R.
Or, in this same Show All window, Control-click (or right-click if you have a multi-button mouse) the item of interest and choose Reveal in Finder from the shortcut menu.
These methods work for most files, but not with Mail messages that appear in Spotlight search results (because Mail messages aren't stored the same way as files in the Finder). However, if you double-click a Mail message in a Spotlight list, the email opens in Mail and displays a "Show in Mail Viewer" link in the upper-right corner. When you click the link, Mail will show you which mailbox your message is in.