As Buck mentioned, there's a version of SP2 for Windows XP available. But it's ~266 megs, while the version that will be up on Windows Update in a few days could be considerably smaller. I'm sort of scratching my head over this one.
While it makes sense in one way - this version appears to be intended for IT people, and I guess it's available now so they can check out the package they'll be using in time to be ready when it becomes generally available. It's sort of flopped in another way, because the IT version *IS* generally available, so people are getting that now instead of waiting.
As far as I can tell, there's a huge group of people perfectly willing to download 140 extra megs today, rather than wait X days for the smaller update to be ready. I may be one of them, depending on when the WU version is ready.
Oh well, assuming the download servers have been up to the demand, I guess that's ok.
There's also BitTorrent sites out there offering a torrent of the IT package. This distribution method has its merits, but there are dangers, and possibly legal implications. Please don't try to obtain SP2 via BitTorrent or any other distributed method if you don't know how to verify the package's authenticity - just imagine the fun an attacker can have with nearly 300 megs of binary to make a trojan with....