Can't erase anymore!

When I open a new hue/saturation layer, the layer mask is white. Isn't it supossed to be black? And when I try to erase a part from the hue/saturation layer, the layer  mask becomes gray, and it's like I erased it for 50%. Also the opacity of my eraser tool is a full 100%. How can I make that I can erase 100%, and that my layer mask is black again?

Click here for a printscreen.

I use PS CS2, but my friend (who's printscreen above) has the same problem and uses PS 7

Thanks in advance.