The following looked simple enough for me.

Source Code

Here a solution, which works for me however you have to be careful since it relies on a certain environment variable to be present. If this environment variable is not available the method automatically assumes the os to operate in 32 bit.

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' @Author - Alexander Bolte
' @ChangeDate - 2016-03-27
' @Description - Determines if a users operating system is of 64 bit or 32 bit.
' In a 32 bit windows operating system the environment variable "ProgramW6432" simply does not exist.
' @Returns true, if the default directory for 32 bit applications is C:\Program Files (x86), else false.
Function Is64bit() As Boolean
    Is64bit = Len(Environ("ProgramW6432")) > 0
End Function

Unfortunately thie below did not work for me as it returned "x86" no matter if I started it on a 64 bit or 32 bit os.

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Sub testArchitecture()
    MsgBox Environ("PROCESSOR_ARCHITECTURE")
End Sub