You all know what it is. Some of apps (Photoshop, AE…) are now compiled for 64bits OS.
This is the pre-release (beta), you can install it while you have CS3 on your system without any problem.
Unpack, burn or mount & install.
1 - Make sure your firewall is properly configured to block the apps from accessing Internet because that shit calls home like E.T.! Your serial will be sent to Adobe to check if it's located in their users database.
2 - As any Adobe pre-release software this one will probably expires after some times, so don't cry when that will happened.