To make this background using CS2.
Open a new file, size 300 pixels X 300 pixels X 300 dpi.

Pick your foreground color (for this blue I used 172db5 as the color) and your background color (030303 used here).

Filter/Render/Clouds=a nice soft blended background. Add additional blank layers and change your colors to fit your needs, add lighting effects, blending modes or paint over the edge area with a paint brush for different effects. Keep your layers seperate to make for easy adjustments.

This will get a nice effect for the background. But this is only a 1 inch square image. To make larger:

Image/Image Size under document size enter the size and dpi you wish it to become. For this sample I made it 10X10 inches at 300 dpi.

Have fun and let me know what cool backgrounds you have made. I would love to see them.