According to the download (ie Automatic Update) its the full release version - and thats whats saying in the System Manager icon, and the v5.windowsupdate.microsoft.com site. So, I think you can take it that its been released - unless it shouldn't have been that is...
Anyway, you can go from XP (no SP) or XP SP1 straight to XP SP2
The download size will probably be in excees of 100Mb though
If you had RC1 or RC2 the download will be slightly less
Apparently it is currently only availiable by automatic download.
Come to the UK Convention on the 23rd & 24th of October