Parking your guest's cars can be a headache, especially when on-the-street is scarce. BNR Valet Parking Service (652-5662 or 588-3747) will do the job for you -- and for your guests -- by scouting the area's vacancies as well as parking the cars. Typical fee for a party of 100: a dollar per guest gets you three valets for four hours. Minimum fee is $36 for one valet for four hours. Bruce Stein, one of three BNR owners, says his crew parks cars for home parties and for business or commercial functions anywhere in the area... You can trim the cost and still have lovely silk floral decorations at your big events. Forever Blooming rents custom arrangements of silk flowers that match your tablecloths or bridesmaids' dresses. Centerpieces that sell for up to $75 rent for $12.50, says owner Susan Katz (Woodley Gardens Shopping Center, Rockville, 762-8833)... Peterson's Annual Guide to Undergraduate Study 1982 is the world's largest college directory, including more than 3,200 two- and four-year accredited colleges and universities here and in Canada. With 2,024 pages, it weighs nearly seven pounds. $13 (plus $2 shipping) from Peterson's Guides, Dept. 5392, Box 2123, Princeton, N.J. 08540... Now Capitol Hill-ites can't complain about bagel deprivation. The newly-opened Chesapeake Bagel Bakery (215 Pennsylvania Ave. SE, 546-0994) has bagels by the bag and in-house seating for bagel snacks.