The font won't help you. each key on your keyboard will represent an individual character rather than the words\sounds that you type being converted into characters. e.g. The hiragana for say the sound 'Na' won't come out as the proper symbol. Two seperate characters for Katakana\Kanji wil come up instead having nothing to do with the Roomaji you typed in.
The font only helps if you have a chinese\japanese keyboard and by that i mean the HUGE keyboards i think they're reffered to as the Big 5 keyboards.
Anyways, short of buying translation software you could always just try finding a website that translates from english to japanese...or ~ i like this option ~ find yourself a nice Japanese girl to help u out...heheheheh.