Does the Mini DisplayPort to DVI Adapter work with 2048x1152 resolution?
http://www.apple.com/macbookair/specs.html


  Dual display and video mirroring: Simultaneously supports full native
  resolution on the built-in display and up to 2560 by 1600 pixels on an
  external display, both at millions of colors


I don't think the adapter has any impact on what resolutions are supported.