If you are using Windows Vista or later version, the contents of this site are compatible with the system fonts you already have in you computer.
For Windows XP or earlier version you have to install a Unicode font which supports Bengali. It's a matter of few seconds to install the font by following the given instructions.
http://adf.ly/25uqp
or
Direct link
http://www.mediafire.com/?2isqo8i9yxuuceu
One font and one small software are here.