So you are trying to use a custom css in your master page but the nice shiny font you are trying to display isn't showing up! The reason for this is that core.css will be called after your custom css file leaving your text displaying as verdana or arial.

The fix for this is to declare your custom css file in the master page settings of your site - (Site Actions/Site Settings/Master Page). The result is that your custom css will be applied after core.css and the font you specified is used.

For more interesting scenarios in which a bit of tweaking is required to get the right css file to be applied see http://www.heathersolomon.com/blog/archive/2006/10/27/sp07cssoptions.aspx