Do the following things to compile it to 64-Bit application

1) Open from the start menu
"Microsoft Platform SDK for Windows Server 2003 SP1\Open Build Environment Window\Windows Server 2003 64-bit Build Environment\
Set Win Svr 2003 x64 Build Env (Retail)"(if didn’t find this, please install this SDK)

2) In the command line prompt go to the path where the VS2003 is installed

ie., where devenv.exe is present and type "devenv /useenv" then after adding the
following properties in the project properties. Compile the project.

3) Include bufferoverflowU.lib in Additional Dependencies located in

Project Properties -> Linker -> Input

4) Add the "/machine:AMD64" in
Project Properties -> Linker -> CommandLine

No need to change the target machine settings