unwanted visible polygon edges

I’ve got a strange problem on my laptop (geforce 4 mx 420 go) whenever there are blended polygons, I can see the edges of the
polygons both from the transparent object itself as well as from others lying behind it.
their color seems to be depending on the blending mode (it ranges from back to white). I have really no idea how this happens.
Maybe someone of you might give me a hint ? I never experienced this problem with my programs on any graphics card before.
I can’t provide you a screenshot, I’m really sorry.
thanx in advance