The upgrade is available from Microsoft's Windows Update and the Microsoft Download Centre, allowing all XP machines to automatically download and install the software.
The company also resumed the distribution of Windows Vista Service Pack 1 on the update services after a problem with Microsoft's Dynamics RMS retail management package.
The issue forced Microsoft to delay XP SP3 release as well as take the Vista SP1 update offline.
A company spokesperson said that Microsoft has put a filter in place for users attempting to download the updates.
This will prevent machines that have the Dynamics RMS software installed from downloading and installing either service pack until a patch can be deployed.
The release of XP SP3 comes less than two months before Microsoft will officially phase out Windows XP in favour of Vista.
System builders will no longer be able to offer XP from 30 June on all PCs except for machines deemed ultra-low cost.
Some vendors, however, have vowed to use a loophole to continue to offer XP to customers.
Microsoft had originally planned to end XP's availability at the end of January. However, increased demand from customers and manufacturers led the company to issue a five-month stay of execution for the seven year-old operating system.
Windows XP SP3 hits the web
By Shaun Nichols on May 8, 2008 7:18AM