It looks like the rumors that SP3 would come out by the end of the month were correct.
from TG Daily
|Microsoft will meet its "first half of 2008" release window for Windows XP SP3, as the entire rollout schedule will be complete by June 10. According to Neowin, Microsoft began support for SP3 yesterday and will send out the OEM version, as well as open it up for volume licenses, MSDN subscribers and Technet subscribers.
The release version will be available on April 29, allowing users to access it with Microsoft and Windows Update, as well as in the company website's download center.
Users who have their preferences set up for automatic updates will receive the service pack update on June 10.