Very different. Not the least bit related.
A jerusalem artichoke looks a bit like a hand of ginger, and tastes like artichoke hearts, sunflower seeds and a little bit like potato. They are truly brilliant when roasted with garlic and pured with butter.
There was a recent discussion about where to find them in Toronto, with fancy places like the Harvest wagon and Sun Valley taking the lead, but some reporting that they'd seen them in Loblaws: