Isn't that guy who teaches us how to bring in the window mail from Vista to be used in windows 7 rather smart?
At the moment, when you click the eml file in your windows explorer, a menu with 'open with' will appear, only by clicking windows live mail, will enable you to preview your email saved in your windows explorer.
Alternatively, windows 7 has an obscure icon on the top right corner of the explorer menu that lets you preview your files, so you needn't open any program to read your saved emails.
hope it helps.