NEW YORK (AP) _ Stocks that have been moving substantially or trading heavily today on the New York Stock Exchange and Nasdaq Stock Market.

NYSE

Southwest Airlines, up 1 1/4 at 18 1/8

The Dallas-based airline said its planes were more crowded in September, and Deutsche Bank upgraded its earnings outlook on the company.

Barnes & Noble Inc., down 3 at 23 1/2

The New York-based bookstore chain, in a bid to expand its computer software and video game offerings, is buying Babbage's Etc. for $189 million in cash. J.P. Morgan responds by cutting its earnings outlook for the company.

Aetna Inc., up 3/16 at 52 11/16

A Philadelphia law firm filed suit against Aetna's U.S. Healthcare unit, accusing the health insurer of withholding vital information from members. The suit is the second of an expected wave of class-actions suits against health-maintenance organizations

NASDAQ

Trend Micro, down 9/16 at 26 11/16

The Tokyo-based maker of anti-virus computer software will provide MCI Worldcom with its anti-virus technology.

ESPS Inc., down 2 9/16 at 5 11/16

The Fort Washington, Pa.-based developer of electronic compliance systems says it won't meet earning estimates due to slow sales of its new products partly as a result of Y2K concerns.

Zomax Optical Media, up 2 9/16 at 34 1/16

The Minneapolis-based providers of services to software publishers said it will beat earnings forecasts because of production improvements.