fresh v. dried turmeric
Grating fresh turmeric will not yield the same stuff as turmeric powder you might buy in a bag. But that doesn't mean that you can't use it.
Turmeric is mainly used for color, rather than flavor. In fact, one problem that novice cooks make with Indian cuisine is the use of too much turmeric, to the point where you can taste it. There are exceptions, of course.
Dried turmeric is usually fried/roasted for a few seconds, but I really haven't found it to make that much difference. The fresh root probably wouldn't hurt if you cook it in oil for 30 seconds, much like ginger root.
Take care in dealing with turmeric, especially the fresh variety when grating. Wear disposable gloves, otherwise your fingers will stain for a few days.