Download is about 330MB and The Final Version will be released early next Year.
Best advice. Wait for that before giving it a try. Going to be several people posting HJT logs with Issues arising from Jumping the Gun and the Bugs are still in the Software! Be Patient! It won't make your machine function faster. May revise some Security settings and give a new utility? (Was the Security Centre and revised Windows Firewall on SP2)
I imagine it'll Link back to Microsofts Site or a "Mirror site" (to cope with demand) As I said earlier don't download this in Haste ..MS are bound to include patches on the Next "Patch Tuesday" (Jan 8th 2008) to rectify Bugs. But a later version will be "fixed"
I would imagine most folk will wait until all kinks have been ironed out. Particularily after the problems experienced by many following the install of SP2.
Betas are best left to those who know what they are about.
I have a disk image to revert to if necessary, so trying out new software/updates causes no problem. I installed the Beta service pack and the OS continued to run OK. The installation created a 583 megabyte backup folder in the Windows directory. I deleted this with no ill-effects, other than this meaning that there'd be no going back (apart from using the disk image). Nothing bad to report about SP3 Beta's installation and usage.
I don't really know but that backup size seems to suggest quite a bit has been done? I didn't notice any differences in operation but there might be some not encountered in my limited use of the computer. This article says something about it.
Provide a new baseline for customers still deploying Windows XP, to help them avoid the inconvenience of applying individual updates.
and
Fill gaps in the updates users might have missed by declining individual updates when using Automatic Updates, and to deliver updates not made available through Windows Update.
For the more technically minded there's a small pdf download.... here....( near the bottom of the page ).