I'm not entirely sure if I have managed to install it or not
I downloaded the file from the above link, then it opened a dos shell thing, and asked me if I wanted to allow windows update to grab SP1.
Next, it downloaded a 4meg file that said it was required to have before SP1 could be downloaded.
Installed that, rebooted, it said no updates available, so I checked again, and this time there was a 4.1meg file, again it said that this was required to download the SP1.
Installed that, and now there's no updates...where the arse is the service pack eh?
Edit: There it is, 5 mins later. 51MB - 519MB
Edit 2: 52.5MB total
Edit 3: Same download, now 77.2megs - weird.
Edit 4: Got stuck at 95% for an hour. Stopped it, restarted it and its installing. Seems this is still very beta-esque at the moment.