First of all, you need to install support for Windows complex script to view complex Asian characters like Bangla. You can download it from here (alt). Run it and install.
Install an Unicode Bangla font. You can download a nice Bangla font from here. Download it and copy that file into Control Panel > Fonts. After copying the font press F5 twice. It will refresh the font list Window.
Configure you browser so that it uses your newly installed Bangla unicode font.
- For Internet Explorer user, go to Tools > Internet Options. Click on the Fonts button. Then select Language Script : Bengali, Webpage font: BNG. Click Ok.
- For Firefox user, go to Tool > Options. Then go to Contents tab. Click on the Advanced under Fonts and Colors option. Select Fonts for Bengali, and select BNG as Serif, San serif and Monospace font.
You are DONE after browser configuration.
For more in this issue under different Operating systems, visit this Wikipedia page or see this post.