Firefox on Windows usually gets it right, if I recall, but it's been a while. It's not a font issue but rather an issue with apps which don't yet support Unicode fully, e.g. being unable to handle conjunct consonants or glyphs which are coded after something they modify but which must be rendered before it visually (e.g. when i modifies a consonant, as in कि ki). Support is getting better as time goes by, and I've happily discovered this evening that Firefox 3 (very close to being released) finally renders devanagari on the Mac.