I think by the start of 2006, Marte is starting in Atlanta. And, until Chipper leaves, I think it'll be in the OF. When Chipper leaves, they'll put Marte back at 3rd.
Langerhans is more of a 4th OF, and even if Kelly Johnson is a starting caliber OF, they have Francoeur to take over in RF.
In 3 years, it would not surprise me to see an OF of Johnson, A. Jones (or Langerhans) and Francoeur, with Marte at 3B. Until then, I could easily see Marte in LF. Regardless, he should be full-time in 2006.