The above registry tweak has been discovered and Microsoft has now closed the 'hole'. You can however still download SP1 using guidelines found at this site:Download Windows Vista SP1 Beta RC Build 6001.17036 v.652 via WebUpdater » My Digital Life
As Mike says please be aware this is a beta and may not be as 'polished' as the final product.

Just to add a footnote. I did try the beta but have since reformatted. It seems it does need some more work and I didn't like what it had done to my machine. To be fair though, Service packs are best installed after a fresh install of the OS and then drivers added. This is especially so with this service pack as the kernal is rewritten. So until I can get a 'standalone' version I'm going to wait.

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