Hi Renato,
This sort of effect is typically done though shaders (occasionally it is also done through billboarded sprites). Vizard has support for GLSL vertex and fragment shaders. I don't have such a shader on hand, but you may be able to find one online if you don't want to program one yourself.
Info on how glow shaders are implemented:
http://www.gamasutra.com/view/featur...ltime_glow.php
Info on writing shaders:
http://www.opengl.org/code/category/C20