Well Gimp has noise (in Filter->Render->Clouds->Plasma), blur (Filters->Blur->... lots of options here) and contrast adjusters, though what you probably want is threshold (Colours->Threshold).

A combination of these would give a more fine-grained control over the end result than the crude selection distort I used above. In fact, you'd probably be able to carry the same method over from photoshop with no problem.

When you do throw yourself into Gimp I'll be happy to provide whatever pointers I can, and others here will do the same I'm sure.