Outlook 2003 SP3 Signatures - How to Create HOVER?

Hi:
I want to create a hyperlink in my signature space with HOVER effect
(change color on mouseover) in Outlook 2003 SP-3. I have tried HOVER elements
both inline and in internal CSS stylesheet using Word 2003 as the advanced
signature editor, but it doesn't work. However, when I dump that code into a
seperate .htm/.html file and test, the hover effect works great. Plus, the
hyperlink in my Outlook signature works fine in an Outlook message. I just
can't get the HOVER effect to work in Outlook. I'm also running Word 2003, if
that matters.
Any suggestions? I'm at my wits end.
Thanks in advance.