One of the "benefits" of HTML is that rendering is left up to the browser (or user). Not only it it not possible to "force" or "lock" the font on every browser, it is not allowed. Even in MSIE/Windows, you can turn style sheets off altogether.
Many browsers, such as Mozilla, allow the user to specify their own CSS. This is a good thing, really. This allows those of us whose eyes are failing rapidly to increase the miniscule point sizes so many designers seem to crave.
AFAIK the only way to force a font is to use images or a plugin such as Flash.