The Thrashers have traded Todd White to the Rangers for Donald Brashear (who will be waived and bought out according to Ben Wright) and Patrick Rissmiller (likely AHL/depth guy). The buyout of Donald Brashear is cheaper than the Thrashers buying out Todd White and it opens up a roster spot for a young forward like Cormier, Klingberg or Machecek (or Pettersson) to make the NHL club out of camp. Or it could also open up a spot for the Thrashers to re-sign Maxim Afinogenov if he remains an UFA as the summer winds down.
Atlanta is effectively getting rid of Todd White and saving roughly $800,000 in real cash. The Thrashers loss some cap space because Brashear's over 35 contract counts fully against the cap, but then again Atlanta has no shortage of cap space. In effect, the Rangers got a player they think might help them and dumped two players they didn't want. The Thrashers deleted an aging injured veteran to clear space for a young guy and saved enough money in the process to pay for that young guy's salary.
Overall a nifty bit of work by GM Rick Dudley of providing opportunities for young players and working towards contending on a budget.