How do I set-up a designed Signature file?

Save your HTML email signature to C:\Program Files\Common Files\Microsoft Shared\Stationery
Open Outlook
Select the Tools drop-down menu
Select Options
Choose the Mail Format tab

In the Message Format area make sure the message format is HTML.

Be sure you do NOT have the "Use Microsoft Word..." options ticked.

In the Stationery and Fonts area click the Stationery Picker button.

You should see your new stationery listed in the drop down list. Select it and click OK.

If you want to change your signature, before clicking OK, select "Edit".  Edit your signature in the small window at the bottom of the page. If you'd like to learn more about changing your default signature or creating a library of signatures, visit this page.

Now click the Fonts button in Stationery and Fonts section. On the Fonts tab, select the radio button that says "use fonts specified in stationery". Click OK. To be safe, also select the font used in your stationery in the Message Fonts/Composting New Message dialogue box. You can also set the reply and forwarding font, as well as when (if) you use plain text messages.

That's all there is to it! Now when you create a new message, Outlook will use your newly installed stationery as your default stationery until you turn this off or select another stationery.