To add an HTML template to Outlook 2007, you must add it as a signature.

When you create a signature in Outlook 2007 it creates 3 separate files (.htm, .txt and .rtf). To create a more custom signature you can write it in HTML - this is especially useful for when dealing with graphics and advanced formatting.

To create a signature in Outlook 2007:

1. In Outlook go to Tools --> Options and the Mail Format tab.
2. Click the "Signatures" button.
3. Click the "New" button.
4. Give your signature a name like, "sig1".
5. Click on OK.
6. Outlook doesn’t require any content to be added and will create 3 files on your computer.
7. Click OK and close Outlook.
8. Locate your signature folder:
   1. Copy one of the following lines depending on what your operating system is.
      Vista:   %userprofile%\AppData\Roaming\Microsoft\Signatures
      XP-2003:   %userprofile%\Application Data\Microsoft\Signatures
      
9. Click on Start and then Run.
10. Paste the line you copied into the Run text box and click OK.
11. You should see 3 files created for your "sig1" file (in .htm, .txt and .rtf formats). If you can’t see the file extensions, go to:
    Tools --> Folder Options --> View
    Now uncheck the "Hide extensions for known file types", or right-click the file and select "Properties" to determine the file type.
12. Replace the .htm file created by Outlook: Take your HTML signature file and use it to replace the .htm file in your signature folder (i.e. save it as in this system folder, using the same filename as the .htm signature file created by Outlook).
13. To start using your new signature, Restart Outlook.
14. Create a new e-mail, then insert the Signature, "sig1" into your e-mail.