I've uploaded the digitally-signed MSI installers for Windows Live Mail and Windows Live Messenger in response to this thread. Using these files significantly reduces the install time and hopefully bypasses some of the errors people have been having.
Download:
Windows Live Mail (Version 12.0.1606) - WinRAR file
Windows Live Messenger (Version 8.5.1302.1018) - WinRAR file
Note: when I test-downloaded these files in Firefox, the filenames get truncated at the spaces and the extension does not get added. The downloads are RAR archives containing the MSI files.