Create file 100x100 pixel. Background White.

Create new layer. Use any selection tool you want (Rectangular Marquee, Polygonal
Lasso...).

Make a selection by creating a shape. Fill that selection with the color
black.

Use the Rectangular Marquee Tool and cut out a part of the layer. Paste it
into the file again as a seperate layer, but put it at the same position.

-->

Then move down the opacity.

Paste the Motif you want to use into the image and use layer blend "Screen".

Duplicate said layer and use layer blend "Overlay".

Create Adjustment Layer:

Layer> New Adjustment Layer> Hue/Saturation

press ok and set the Saturation to -100.

Create new Layer and choose one of the brushes in this
brush set.

(You can create similar brush sets using the text tool and repeating the dot
over and over again. To learn how to save the brushes, please refer to
www.smallvillefanart.com and use the Tutorial section.)

Use the brush on the layer choosing color white. Adjust Layer Opacity to
your liking.

Choose text tool. Choose font ChromosomeLight (Download
here) and add desired Text.

Then I adjusted it a little bit using gradients....

or http://www.ex-posed.com/icon/tutorials/tutorials.htm

ps: this is kindo fo modled after an icon I saw somewhere... bu I don't remember where that was.