We keep receiving questions about Visual Studio 2005's support for 64-bit.  Here is a set of factoids that should help answer the most commonly enquired issues:

(a) There are two flavours of 64-bit - AMD64 or X64, and IA64.  Windows 64-bit installs on both architectures.

(b) There is no 64-bit version of VS. Visual Studio 2005 is available only as a 32-bit app.  However, you CAN install VS on a 64-bit OS and use it to create, launch and debug 64-bit apps. 

(c) VS will install only on X64.  The .Net Framework and the Debugger components install on IA64, allowing you to remotely launch and debug applications on IA64 from a VS IDE installed on another machine.

(d) VS installed on either 32-bit or 64-bit OS can create 32-bit or 64-bit applications, but of course the applications need the corresponding platform to execute.

(e) You need the Professional or Team System versions to build X64 (AMD64) apps. 

(f) You need Team System to build IA64 apps. Pro does not support this. See http://msdn2.microsoft.com/en-us/library/hs24szh9(VS.80).aspx

(g) On a 32-bit OS, the 64-bit compilers will not be installed by default, you will need to go to custom setup and check the option.

How to create 64-bit apps

A managed project is automatically built according to the architecture selected => default C# project created on AMD64 will be AMD64, X86 on X86.  The native one is always 32-bit by default.

To explicitly set a platform:

(1) open the solution explorer, select solution, right click->Configuration Manager.
(2) go to 'Active Solution Platform', click New.
(3) in the 'New Solution Platform' dialog that comes up select the new platform say Itanium. Set 'Copy Settings From' to 'Any CPU' which was the default setting in the 'Active Solution Platform'.
(4) click OK.

You will see that the platform has changed to Itanium in the config manager.  Now when you build the  solution, you will get an Itanium exe.

Follow the same process for X64, and to rebuild 32-bit apps from that solution.