Betas.intercom.net As far as i have seen this isnt posted on any other site, so here it is!!

Microsoft continually works to improve its software. As part of this effort, we develop updates and fixes to recognized issues and release them for customers. On a regular basis, we combine many of these fixes into a single package and make the package available for you to install on your computers. These packages are called Service Packs.

Official Windows XP Service Pack 1 website and Download