As I had posted earlier that Vista SP1 RC will be available to everyone for download, Microsoft released it today
You can grab the RC Windows Update script here
Believe it or not, Windows Update has been the best and easiest way to get Vista SP1. We beta testers have had good success installing SP1 Beta releases and RC via WU.
You may be required to install at least 3 updates before the Service Pack. After installing those pre-requisites, restart your machine (if required), wait for at least 10 mins or so and then check for updates again. You should be prompted for Service Pack update.
To discuss regarding SP1 and to submit bugs, please visit here