I've been looking at this. Here's a couple things.
In the view source for your skin demo page, there is a SPAN with a dnn_dnnMENU ID. There is a call to fonts there that begins with FontStyle="font-family:....". It looks like where you have FontStyle, you might really want just "STYLE" and then ="font-family:'arial narrow', tahoma," etc. ALSO the end of that style statement ends with a text-decoration: that doesn't finish. It might need a "none" and it's probably good to end it with a semi-colon; and then close quotes.
I'm not certain about the call to arial narrow with the single quotes or no quotes. You'll have to see after you fix the statement, but if you're seeing Tahoma (as I am) it would stand to reason that the browser is ignoring the 'arial narrow' call. To me it looks like Tahoma 12pt which is what's next in your STYLE statement. You could try an underscore for the space maybe - but it seems to be ignoring it now.
Also, I would do a project wide search for "FontStyle" because I saw it in a view source for another page there so it could be causing problems even if you fix it in the source code for this skin demo page.
I think that's it - Try it out.
Alternately, according to one of my books, the attribute could also be "fontnames" So it could be fontnames="'arial narrow', tahoma, arial, helvetica;" and then fontsize as an attribute with a number and fontbold="true or false"
David - recently skinning