The universal passion to peep in other people's windows is responsible for the success of house tours. But not many windows are as beautiful as the bay, at right, hung with a contemporary tapestry - a dandelion worked in wool on swiss organdy - by fiber artist Nancy Hemenway. Hemenway also designed the pottery on the table: the bird casserole and the butterfly plates. Other handsome embroidered paintings by Hemenway will soon be exhibited across the country. The Georgetown house Hemenway shares with husband Robert D. Barton is also embellished with embroidered pillows from a stitchery school she began when her husband was a Foreign Service officer in Mexico, "and I didn't want to work in a thrift shop or play bridge." The pillows and evening skirts are sold in boutiques in this country and form a substantial part of the small Mexican town's income. Hemenway started as a portrait artist and turned to the needle when faced with the difficulty of transporting oils and easels in the Foreign Service. The Hemenway/Barton house and the home of Sheila and Edward Weidenfeld, below, are two of the houses on the annual Georgetown House Tour, six houses each on Saturday and Sunday of this week. The photos are by staff photographer Douglas Chevalier.