Peterson has more value by the trade deadline than JJ, he can actually score and play D. So the Knicks may still get his contract off the books.

Ditto. First deal works to get JJ outta here. Forget the second trade. Our PG of the future is Ricky!!!

Or Lebron.

Why do we need the second trade?
Let me attempt to answer that question, it may take a while.
When I look at the roster, we have 3 major holes. pg, sg and c.
Duhon is a back up at best. Hughes is the only legit sg on the roster but he is streaky. Lee is not a center.
What does Lebron see when he looks at the roster? There is a legit PF in Lee but he can't play D, promising players in Gallo and Will, an undersized combo guard in Nate, a feel good story in Bender, and JJ (I am not even sure what he is supposed to play on the team, pg defender extrodinaire?) A couple of rookies that can't get any burn on a non playoff team in TD and Hill. That's all there is. I am not sure that's good enough to sell Lebron to come. Given all the intangibles NYC provides, Knicks are still rebuilding and it is tough to tell him to sign and be patient, he still wants to win.
The second trade addresses that. In one fell swoop, by replacing JJ with Peterson, we take care of 2 positions, pg and sg. The cap issue improved a bit but the roster improved a lot.
We solve our pg issues for the next 10 years with Collison. Peterson is 31, he has a couple of good years left. That will give us just enough to time draft and groom a stud sg.

What happens to the Center postion you may ask? Well that's where the 3rd trade comes in;
Lee, Will + fillers for Bosh (No effect on the 2010 cap, Lee's cap hold + Will is about a 15 mill)

2010 roster:
PG: Collison, Brown
SG: Peterson, rookie
SF: Lebron, Gallo
PF: Gallo, Hill
C: Bosh, Bender

We lose all the expirings. Trade Nate, Al for picks. The rest, I could care less.
By the way, if by any chance we cannot get Lebron, it is still a good team that can do some damage in the east and Curry's deal will be expiring in 2010.