Check out our Diddy/Dirty Money section for more posts about Diddy/Dirty Money.
Diddy and Jd. But why is Diddy rappin about NYC?
According to a press release and the 2010 VH1 Hip-Hop Honors website, Diddy was added as a last minute performer for the show, which will air on VH1 on June 7 at 9 PM ET.

The show will honor The 2 Live Crew, J. Prince, Jermaine Dupri, Luther "Luke" Campbell, Master P, Organized Noize and Timbaland. It's unclear who Diddy is performing in honor of, but it's being taped this evening and CEO Chuck Creekmur posted the photo above (click to enlarge) of Diddy on stage with Jermaine Dupri and said that Diddy was rapping about New York City. I'll take a wild guess and and say they were performing the "Welcome to Atlanta" remix.

Update: Creekmur confirmed to me that the song was, in fact, the "Welcome to Atlanta" remix.