2007 is undoubtedly the Windows Vista year for Microsoft, but with Windows XP sneaking in to crash the Wow party. XP has in fact been the sole catalyst of rain on Vista's parade this past year, as the two operating systems have been involved in an intimate tandem from the market share face-off, to comparisons focused on the adoption rate and to the service pack measuring context centered on performance. But if 2007 has been anything, then it has been rich in free Windows downloads from the third and final service pack to Windows XP to the exclusive Enterprise SKU of Windows Vista.

On December 19th, the Redmond company made available to the general public the first public version of Windows XP SP3. The Release Candidate for XP PS3 signals Microsoft's proximity to delivering the final version of the service pack in early 2008, alongside Windows Vista. You will be able to download and test drive XP SP3 RC via this link. Be advised that Build 3264 is still a beta version, despite the RC label.

XP SP3 RC was just the latest item in a series of releases for both the Windows client and server products. Earlier this month, Windows Vista users finally received access to the Vista SP1 Release Candidate. Almost simultaneously, Microsoft also dropped a new development milestone for Windows Server 2008, formerly codenamed Longhorn. You can grab the Release Candidates of Vista SP1 and Windows Server 2008 here and here.

December is also the month when the Redmond company updated its free offerings of Windows XP SP2. Web developers and not only, can enjoy two Virtual PC images of XP SP2 pre-activated and optimized for use with a virtual machine. Both virtual hard disks are time bombed and set to expire on April 1st, 2008, at which time Microsoft will probably release fresh versions. The VPC images are here.

And to top it all off, Microsoft is also offering free trial versions of Windows Vista Enterprise. The Enterprise edition of Vista is reserved for Microsoft Software Assurance customers via volume licensing. But, any user can download two VHDs of Vista Enterprise and give the SKU a try for a whole month.