My answer was based on your questions there is no difference when installing SQL Server 2005 either x86 or x64, in 2005 the only thing to look for is make sure all your web use for IIS6 to be x64 or you have to run IIS 6 in x86 mode because you cannot run IIS6 in both x86 and x64 modes. If you are not running SSRS it is simple install if you are running SSRS make sure you add IIS6 and click on details to enable features needed to run Asp.net because SQL Server 2005 installer will disable SSRS if IIS is not running.