Millwood was acquired from the Crik Rats along with Kerry Lightenberg and Bill Taylor for Shane Reynolds during the 1998-1999 offseason. Millwood was initially the least important component of the trade, since the Zingrods were desperately trying to replace Mariano Rivera with a cheaper closer.
As it turned out, early stints on the DL by Francisco Cordova and Denny Neagle increased Millwood's significance considerably. Plus, Lightenberg notwithstanding, it's hard to go wrong with a Braves pitcher.
Update 10-14-1999: Looks like the Braves have a new ace. #3 on the Zingrods "1999 Pleasant Surprises" list behind Mike Lieberthal and Fernando Tatis. Millwood was 100% pleasant to have on the roster, but he simply wasn't as big of a surprise as the other two. Unfortunately, his salary was a bit too rich for the Zingrods' blood, and he was released in the 1999 offseason.