While Eddy Curry played surprisingly well in his two-game stint in Dallas, cutting him to pick up Troy Murphy should end up working to the Mavs benefit.
Murphy, an 11-year NBA veteran, has averaged 11 points and 8 rebounds over his career. His per-game statistics have taken a dramatic slip in the last few years, but he could still be a very effective player in Dallas.
A 6'11 245 "stretch 4", Murphy has made a career playing average defense and spotting up on the perimeter, "stretching" opposing defenses by dragging his defender out of the paint. If you think about it, you can see why a player like that would retain value well into his 30's: height and shooting ability aren't really affected by age.
Last year, in LA, he was the victim of a minutes crutch at the big man positions. The Lakers gave heavy minutes to both Andrew Bynum and Pau Gasol and had a much younger version of Murphy (Josh McRoberts) taking any available minutes off the bench.
After his efficiency statistics dropped completely off the cliff in 2011, he rebounded in 2012, albeit not in very many minutes: 45% from the field, 42% from beyond the arc.
As a veteran of five teams, you would expect Murphy to be able to figure out the Dallas playbook fairly quickly, so conditioning will probably be the biggest factor affecting how quickly he could help. He probably won't be in game shape and may need a few weeks to get into more of a rhythm.