How can i make a glow effect only for one object?
If you are using 2.5, you can simply enable indirect lighting in world buttons, and give your material an emit value. other than that it can be done with composite nodes and render layers, or with linked scenes and the sequence editor. i think there are a couple tutorials on making lightsabers, you might try looking for those.
(edit) if you opt for indirect lighting, set to ‘approximate’ since raytrace doesn’t work yet.