Scripting

If anyone's curious, this is how I ended up doing it:

Set WshShell = WScript.CreateObject("WScript.Shell")
OSArchCheck = WshShell.RegRead("HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment\PROCESSOR_ARCHITECTURE")

If OSArchCheck = "x86" Then
	WshShell.Run "msiexec.exe /qn /i install_x86.msi /norestart"
Else
	WshShell.Run "msiexec.exe /qn /i install_x64.msi /norestart"
End If

@nivek03

I started using autohotkey for all my scripts because things like this are not easily possible using bat/cmd scripts.  This is what I use to detect 32 bit on 64 bit architecture. (autohotkey scripting language)

IfExist, C:\Program Files (x86)\*
{    
    Run 64bit_App.msi
} else {
    Run 32bit_App.msi
}

Simple.

if "%PROCESSOR_ARCHITECTURE%"=="AMD64" goto AMD64

if "%PROCESSOR_ARCHITEW6432%"=="AMD64" goto AMD64

if "%PROCESSOR_ARCHITECTURE%"=="x86" goto x86

:AMD64

msiexec /i your_x64.msi /q

exit

:x86

msiexec /i your_x86.msi /q

exit

Powershell and WMI:

$os=Get-WmiObject -Class Win32_OperatingSystem

if ($OS.OSArchitecture -eq "64-bit")
{
    Do something
}

Without WMI (not tested, but should work): 

if ($env:PROCESSOR_ARCHITECTURE -eq "AMD64")

{

    Do something

}

look at: (see if it helps)

http://www.codeproject.com/Articles/73000/Getting-Operating-System-Version-Info-Even-for-Win