All you have to do to achieve glow in pixelmator:
1) Take an image
2) Duplicate the layer (Make sure View/Show Layers is on, then Right click/Duplicate)
3) View / Show Effects must be on. From the little Effects window, choose Gaussian Blur. Make it something like 10-15px of blur radius. Your duplicate layer should look like that:
4) Under Blending in your Layers dialog select LINEAR DODGE, then drag the opacity to get your desired level of glow. Make sure the blurred texture appears ON TOP of the original.
5) The result should look something like that