Google has unveiled a beta version of its long-awaited desktop search application, built with the same technology that powers its internet search site.

Google Desktop Search is free, downloadable software designed to let users search local PC sources. It can retrieve data contained in Microsoft's Outlook, Word, Excel and PowerPoint applications, as well as instant messaging sessions conducted with AOL Instant Messenger.

The software also lets users retrieve content from web pages viewed with Internet Explorer. When a user views a web page, Google Desktop Search automatically caches its content so the user can later see the same version of the page, even if its live content has been altered.

The market for searching desktop resources is not new – Google has competition from a number of niche players such as blinkx, Copernic, ISYS Search Software and X1 that offer alternatives to the basic email and file search functions built into Microsoft's systems.

But there's been a growing fervour surrounding the technology in recent months since big guns Google, Microsoft and Yahoo indicated their intention to tackle desktop search. Notably, Google is the first of these titans to deliver a working version. Microsoft demonstrated its own revamped desktop search technology this summer, but didn't share its expected release date.

To get started, Desktop Search indexes a user's hard drive. This process could take several hours, but it occurs during times when the computer is idle, Google says. The software then continuously scans for new content and adds it to the index. When a user downloads a new email in Outlook, for example, Desktop Search can find and index it within seconds, the vendor says.

Once the initial indexing is complete, users can choose to run a search using the website, so that both PC and web sources are searched simultaneously. When a user searches through, Desktop Search runs the same search in parallel on the user's computer. If Google Desktop Search finds relevant results, those results appear on the search results page, flagged as coming from the user's own content sources.

Alternatively, users can bypass the Web and search for local information by accessing Google's software from the Windows taskbar.

Google Desktop Search is available