For Outlook Express:
Right click and "Copy" the E-Mail Signature of your choice.
Open Microsoft Outlook
In the "Tools" menu, select "Options"
Select the "Mail Format" tab and click "Signatures"
Click "New"
Enter a name for your signature and choose "Start with a blank signature"
Paste the image in the body and click "Finish"
When you return to the "Options" box, be sure to select your STOMP signature in the "Signature for new messages"
Click "Apply"

For other e-mail providers:
Right click and "Save Picture As"
Add the file as an attachment