Now that Windows 8 has hit RTM there is a slightly newer version of Orca the MSI editing tool available. This one is version 5.0.9200.0, but when it’s installed, in the Programs and Features dialog it’ll show up as 8.59.25584.
To grab yourself a copy get the Windows SDK for Windows 8, install using the option to ‘download for installation on a separate computer‘, and make sure only ‘Windows Software Development Kit‘ is selected in the features list. You won’t be able to de-select the .NET 4 download.
After your download is complete you can either install Orca from the download directory, or collect up the files you need to keep a copy for use later on. The files you’ll need are listed here and are linked directly to Microsoft download location for ease of collection:
To install Orca just double-click on Orca-x86_en-us.msi and allow it to install. Job done!