How can I run an exe in 32-bit mode on a 64-bit machine?

How technical an answer do you want? You can probably force the exe to always run 32bit with a few SDK tools, but it does require a little work.

The easy answer is to launch from a 32bit process (eg. use %SystemRoot%\SYSWOW64\cmd.exe to launch).

The more complex is to check what kind of exe it is, then modify it yourself. Background here is to understand that compiled code from languages that directly work with the Windows APIs are created as 32bit or 64bit at compile time by the developer. This cannot then be changed without going back to the source code.

However increasingly applications are written via a virtualisation layer that makes writing applications easier. There are two common ones: .NET and Java. I'm not sure about Java except knowing that forcing the right Java runtime install with solve the problem.

For .NET you can use SDK tools to:

• Validate that the application is "AnyCPU": corflags myExe.exe. Using a utility from the .NET SDK to read the headers of a .NET assembly, for an exe will return something like:

Version   : v4.0.30319
CLR Header: 2.5
PE        : PE32
CorFlags  : 0x20003
ILONLY    : 1
32BITREQ  : 0
32BITPREF : 1
Signed    : 0

the 32BITREQ tells me this is AnyCPU because 32bit is not required.

• Use corflags with its /32BITREQ+ option to modify the exe to be 32bit only.

If you have windows 7 professional (or higher), then use the virtual XP mode from Microsoft

this emulates(?) a 32 bit environment, and it has proved useful for getting some old 16 bit programs to run