The ESPN "trade machine"
http://games.espn.go.com/nba/features/trademachine
shows the Knicks over the cap by $33.7 million. It also reports that Marbury is likely to be released if the Knicks aquire a point guard.
The Knicks are stuck with Zack Randolph ($13.3 million) and Jamal Crawford ($7.9 million) for 3 more years, and Eddie Curry (8.7 million) and Quentin Richardson ($8.1 million) for 2 more years. Shedding Starbury's $19 million will definitely help. Getting far enough under the cap to sign a big name free agent in 2010 will gut the team for the next 2 years. What incentive would that be for Bosh or Wade or LeBron to come? Paul won't be free that year.
Good luck trading Zack Randolph. Memphis and Minnesota may be the only franchises dumb enough to take his contract and attitude. Oh wait, the Bobcats may also be that dumb.
The big reason to get rid of Starbury now is to get rid of his attitude and start the D'Antoni era on the right foot.