Google Desktop indexes all a computer's resources, thereby providing instant search functionality.
The results are presented just as ordinary search results in Google, and are much easier to read and review found files.
Google Desktop also allows you to search the web pages you've been browsing, even when you're offline. The entire PC will be compressed into a mini-Google web browser.
Examples of the local resources on Google Desktop are: Outlook and Outlook Express, Word, AOL Instant Messenger, Excel, Internet Explorer, PowerPoint, TXT, etc.