What is the difference between fibromyalgia and scleroderma?

Huge difference. The difference is huge: scleroderma is an autoimmune disease in which the body attacks itself & causes the skin to become hardened, decreasing the patient's mobility. It can be local or body-wide. Fibro is not considered autoimmune. In fact, there is no real agreement on what fibro actually is, though its hallmark is pain all over the body, often with severe fatigue. The 2 disorders can coexist.
A lot. These diseases are of of different mechanisms. Fibrimyalgia appears to be overactivation of the persons nervous system, where the pain threshold is lowered. Scleroderma is a autoimmune disease, where the body creates antibodies that attack the connective tissue, ie:p skin collegen, etc. And it can effect the whole body.