Are parts of XP SP3 already available as standalone downloads?
Yes. A few fragments of XP SP3 can already be accessed by XP SP2 users, but Microsoft will include them into the third and final service pack for XP. The features include the MMC 3.0 framework, MSXML6, Windows Installer 3.1, Background Intelligent Transfer Service 2.5, IPsec Simple Policy Update for Windows Server 2003 and Windows XP, Digital Identity Management Service, Peer Name Resolution Protocol (PNRP) 2.1 and Wi-Fi Protected Access 2 (WPA2).