That’s right! Now you can get your hands on the first Release Candidate for Windows XP Service Pack 3! And all it will take is the implementation of a simple registry hack designed to allow Windows XP users to access, download and install Service Pack 3 Release Candidate straight from Microsoft.
You are not one of the 15,000 testers that have been so far permitted access to the RC build? No problem. And on top of that, there is no need to wait for a public version of one of the upcoming development milestones of XP SP3.
If you really can’t wait to get your hands on XP SP3 RC, then all you have to do is play around with the registry a tad.

More information [Softpedia]