Prior to upgrading you will have to remove the previous SP1 Betas and Release Candidates (RC1/build 6001/KB936330). I will detail the RC removal as that is what I have and can't speak for the betas. You can do this the automated way via "Programs and Features" removal or you can go the manual route via the command prompt.
Automated: Start->Control Panel->Programs and Features->View Installed Updates then uninstall "windows vista service pack - KB936330".
type "cmd" in the Search box under the Start menu and right-click selecting "Run as administrator" from the contextual menu that will pop up. Identify the build number of your previous Vista SP1 installation and put in the following command: "start /w pkgmgr /up: VistaSP1-KB936330~31bf3856ad364e35~x86~~6.0.0.". This is obviously valid for 32-bit machines. On 64-bit computers replace "x86" with "amd64". For confirmation enter "winver" and press Enter in the Run dialog box.source: news.softpedia.com
On a side note...if you do plan to upgrade to Vista...GO FOR THE X64 VERSION. It really doesn't make any sense to upgrade to the 32-bit version at this point...go for the version with room to grow...X64.
UPDATE:: Be ready for this SP1 update to take an hour to install from start to finish. Hopefully you will get this bad boy via automatic updates and don't have to wait.
Vista SP1 x32 (32-bit)
Vista SP1 x64 (64-bit)