Place the potatoes in a vegetable steamer or a basket set over boiling water. Do not let the potatoes touch the water. Cover and steam for 10 to 12 minutes, or until tender when poked with a sharp knife. When they are cool enough to handle, cut the potatoes into quarters.
Combine the potatoes, celery, and onion in a large bowl, and season with salt and pepper. Toss with enough dressing to moisten potatoes, and serve.