Microsoft on Friday released the first of two expected final testing versions of Windows XP.

Despite the turmoil created by Thursday's appeals court ruling, the Redmond, Wash.-based software company completed Windows XP Release Candidate 1 days ahead of schedule. Availability of the release candidate comes just days after Microsoft and 600 partners, including retailers and PC makers, met in Las Vegas behind closed doors. While few details emerged from the non-disclosure Windows XP marketing meeting, Microsoft revealed that combined the group would spend as much as $1 billion promoting the new operating system. Windows XP, which debuts on Oct. 25, will ship in two versions: Home and Professional. Basic features--among them Internet Explorer 6, Windows Media Player, Windows Messenger and Internet firewall--are essentially identical. The Home version is the upgrade to Windows 95, 98 and Me, while Professional replaces Windows NT and 2000. According to the release notes accompanying the software, Microsoft recommends a PC with a 233MHz Pentium processor and 128MB of RAM. Release Candidate 1 will be distributed as part of the Windows XP Preview Program. People signing up for the program pay $9.95 to download the about 500MB preview release, or an extra $10 to receive a CD by mail. Those subscribing to the program will need a valid code from Microsoft to activate the software--essentially locking it to their PC configuration--or Windows XP will stop working after 14 days. Windows XP automatically guides users through the process, which is completed over the Internet or through a phone call to Microsoft. The first release candidate is feature complete, including support for HailStorm, one of the cornerstones of Microsoft's .Net software-as-a-service strategy. Through HailStorm, which relies on Microsoft's Passport authentication system, the company envisions delivering content and services to a wide range of devices, whether they be PCs, handhelds or cell phones. Passport authentication is required to use several features, including Windows Messenger.