VPSKEYS is a software provided by the Vietnamese Professional Society. It allows you to type Vietnamese diacritic symbols from your keyboard. It is fully customizable to the keys you like. You have full control of it, turn it off/on when you need it. You can use Unicode fonts, meaning you don't have to install any special fonts. The prefered fonts to use is Unicode as most Windows built-in system fonts are now Unicode compatible.

Download VPSKEY. Read the VPSKEYS user manual from the VPS if you have any setup issues.

Be sure to set "bản mã" to unicode and use fonts such as Arial, New Times Roman, Tahoma, or Verdana.