I had the need to detect if a system was running 32 or 64 bit, I ended out with a solution much like the one shown below;
Just create two subdirectories called X86/X64 (X86 version in X86 and X64 in X64) and then create a install.cmd in each to install either the x86 or x64 version.
@Echo off if defined ProgramFiles(x86) goto INS64 goto INS32
:INS32 Echo 32 bit installing call x86\install.cmd goto END
:INS64 Echo 64 bit installing call x64\install.cmd goto END