DailyApps.net (opens in new tab) has tested a method that allows legitimate Windows XP users (Home, Professional and MCE editions) to download SP3 RC1 directly from Microsoft.
In the light of reported increases in performance, this might be a download well worth trying, although you will be left to your own devices if something wrong happens.
The trick only takes a few seconds and requires you to download and run a file which will make Microsoft think that you are part of its Private beta Program.
Apparently, The hack only works with 32-bit version of US/English Windows XP.
According to some sources, Windows XP SP3 will feature 113 security updates and 985 hot fixes but will not include (opens in new tab) any major new features, but it will include four minor new features that improve the system’s reliability and security.
As for all Release Candidates and Beta software, you are advised to backup your important data (including your serial numbers) before installing the SP3.