at my computer (Dutch win7 ultimate 64 bits) the blender.exe file can't be opened.
I downloaded "Windows Blender 2.5 alpha2 x64" from the blender.org site (http://www.blender.org/download/get-25-alpha/).
then I copied the .rar file to c:\ and right clicked on the file and clicked on 'extract here' (I have winrar installed).
A new folder appears called 'Release'.
When i open it i see very much folders and files including blender.exe
I click on blender.exe and get the error you can see in the attachment.
very, very simple translation:
"The executable could not be started because the sideways configuration is not right.
See the log Executable or use commandprogram sxstrace.exe for more information."

if you don't understand my english get to google translation and type in the dutch and click translate. :)

NOTE: everything works fine with the 32 bit version!!!