make light pixels transparent

Hi,

I"m taking a logo PNG file and darkening the pixels around the edges (via contrast) of black text. But now that I have more contrast, I want to take the remaining light pixels and make them transparent (the same extent that they are white).

I'm a complete amature, but determined. So keep that in mind when you give directions.

Using PS 6.

Here's a screen shot so you can see what's up.I want to make those shiny parts be part black and part transparent (for whatever background).