What version of Outlook are you using?
In Outlook 2003, the following works:
1. Tools - Options - Mail Format
2. Set Compose... format to HTML
3. Click Signatures at the bottom.
4. Click New.
5. Name it, and choose Next.
6. Click Advanced Edit, and say Yes to launching a non-Outlook editor.
7. Here, this brings up FrontPage. If you don't have FP, it'll bring up your
default HTML editor. Use this to insert a .jpg, .gif, etc. of your
signature; save & close the editor.
8. Etc... I assume you know the steps from here.
When I make this signature the default, and set Word as my editor, the
signature appears when I start a new email. It also shows up when using
Outlook at my editor.
Caveat: zillions of email users tell Outlook (et al) to read all email
messages as text only... because they find others' choices of fonts annoying
(usually the point size is set too small), because they don't like
embedded/automatic links, because they don't like animation/color, etc. They
probably won't see your signature.
Another reason NOT to do it... do you REALLY want a copy-able version of
your legal signature in circulation on the internet? Unless you're sending
it to people you trust 100%, it's not be a good idea, and makes identity
theft one step easier.