Error: Tag not found in currently active versions - cross platform help

I added two tags, <emph> and <note> to a css style sheet I am using to create a web site.  The first tag I use to emphasize certain words or phrases while the second is used to call out notes.  They look like this:

note {
font-style:italic;
color:#FF0000;
font-weight:bolder;
font-variant:small-caps;
}

emph {
font:"Courier New", Courier, monospace;
font-weight:bolder;
color:#006600;
font-size:18px
}

When I view the site in Chrome or Firefox, it looks fine.  The text I have formatted with the above tags is perfect.  In internet explorer however they are not working.  Anything formatted with the above tags does not display with the tags style settings, they are shown with the sites default font settings.  A sample line of code reads:

<note>*NOTE: Please read this step in its entirety as it contains time sensitive steps</note>

Which should display the line in Red bold text, with small caps.  It does in Firefox and Chrome but not in IE.  Same goes for anything with the <emph> tag.  The style is just ignored.  When I try and validate the site I get the error:

The tag name: "emph" Not found in currently active versions.[HTML 4.0]
The tag name: "note" Not found in currently active versions.[HTML 4.0]

Does anyone have any idea what the problem could be?  Just fyi, I am building the site with Dreamweaver CS3.