While mushrooms soak in 2 cups water, saute onion and garlic in oil until golden and transluscent. Stir in wine and rinse, drained barley. Cover and cook for 10 minutes. Drain and slice the mushrooms, reserving the liquid; add both to the pot of barley. Add salt and cook for 10 minutes. Add 4 cups of boiling water, one cup at a time, cooking pilaf 10 minutes between each addition. Stir in parsley, vinegar and pepper with last cup of water. Simmer on low heat until all the water is absorbed and the barley is tender.
