NEW YORK (Standard&Poor's) Aug. 13, 2003--Standard&Poor's Ratings Services said today that it assigned its 'AA-' senior unsecured debt rating to pharmaceutical firm Bristol-Myers Squibb Co.'s offering of $400 million 4% senior unsecured notes due 2008 and to the company's $600 million 5.25% senior unsecured notes due 2013. At the same time, Standard&Poor's affirmed its 'AA-' corporate credit and senior unsecured debt ratings on Bristol-Myers, as well as the company's 'A-1+' short-term corporate credit and commercial paper ratings. The outlook is negative. "The continued superior investment-grade ratings on New York, N.Y.-based Bristol-Myers reflect the company's strong presence in the worldwide pharmaceutical industry, its diverse product portfolio, and its solid financials, factors partially offset by the