I successfully followed this Photoshop tutorial the other day to create a base effect for a desktop wallpaper I had in mind:

http://www.photoshopessentials.com/photo-effects/punch-through/

I was able to replicate most of the steps, however, for some steps, there are features that don't exist in Gimp, so I had to improvise with workarounds. If you're an intermediate Gimp user, then you should know how to work around them. Here's my result: