Off the top of my head, Inno Setup can select 32-bit or 64-bit installs. The Inno installer uses a config file. I've never used Inno, so I don't know what is involved in creating that config file.
If you don't need a one-size-fits-all installer then you could have a seperate installer for each word size. You could then use an easy, wizard-based installer like InstallForge or InstallSimple to create those installers.
If you don't need a one-size-fits-all installer then you could have a seperate installer for each word size. You could then use an easy, wizard-based installer like InstallForge or InstallSimple to create those installers.