Yeah, now we have the Windows 2008 SP2 and Vista SP2 in RC version, if you are an MSDN suscriber or Technet Plus, you will be able to download it!, in any case check all the changes in: http://windowsteamblog.com/blogs/windowsvista/pages/notable-changes-in-sp2-rc-for-windows-vista-and-windows-server-2008.aspx
To install just be sure that you have the SP1 installed before (remember that for Windows 2008 is already 'included').
And these are the notable changes on the RC:
- Application Compatibility improvements: they improve even better the compatibility of applications, meaning that we should have less problems!
- Hardware ecosystem support and enhancements, if you follow the Windows 7 improvements, then one feature will be familiar, since SP2 improves performance for Wi-Fi connections after resuming from sleep mode, also it includes updates to the RSS feeds sidebar for improved performance and responsiveness (finally!!!!), there are another improvemets, support to record data to Blu-Ray media, support for 64-bit CPU for VIA, includes Bluetooth 2.1 and WCN (Windows Connect Now)
- Operating system experience updates, includes Windows Search 4.0, improves the Windows Media Center and make a tweak on the registry for application compatibility.
- Enterprise improvements, SP2 provides the Hyper-V virtualization environment that doesn't mean that you can run Virtual machines there, but that you can manage all the Hyper-V environment, that is very different!, it also improves power management (now you can manage via GPOs!), increases the authentication options for WebDAV redirector and improves backwards compatibility for Terminal Server license keys.
- Setup and deployment improvements, is a single installer for Vista or Windows 2008!, includes better error handling (yeah!), and others, but the cool thing is that it includes a tool called Service Pack Clean-up (Compcln.exe) which helps recover the hard disk space by permanently deleting previous file versions (RTM and SP1) that are being serviced by SP2.
Finally remember that the RTM right now is planned for the second quarter of the 2009!.. so plan accordingly!