UPDATE: 04.24.2015 - For an update on how the Tool Viewer Release affects these systems, visit this blog.
We have made some changes to the Second Life System Requirements to bring them more up to date, and are making some related changes to the Viewer:
We have removed Windows XP and Mac OSX 10.6 from the list of supported operating systems. Microsoft has announced the end of support for XP, and it has been some time since Apple has released updates for 10.6. For some time now, the Viewer has been significantly less stable on these older systems, and the lack of security updates to them make them more hazardous to use.
We have no plans to actually block those systems, but problems reported on them that cannot be reproduced on supported systems will not likely be fixed.
The Windows installer has been modified to verify that the system has been updated with the most recent Service Packs from Microsoft. While we will not block installation on Windows 8 at this time, we strongly recommend upgrading to 8.1 for greater stability. Our data shows that the Viewer is significantly less stable on systems that have not been kept up to date, so the installer will now block installation until the updates have been applied. This change will be effective in a Viewer version to be released in the next few weeks, so it would be a good idea to get your system up to date before then. You can find information on how to install the latest updates at the Microsoft Windows Update page.