I downloaded a Batmobile tumbler 3d model from free3dmodels.com.The model was in 3DS format.I converted the model from 3DS to mdl file in MED.But whenever i open it, it gives a warning:Error E1308: BATMOBILE.MDL: Bad mesh - more than 64K vertices:Program aborted.So please can anyone tell me what to do to make it work.

you need some polyreducer to get this model useable
but you won't get happy with this kind of model because they have way to many polygons to use them in games
your model should have about 6k-8k polygons to get the best framerates

mdl format simply cannot handle more than 64k vertices, so you can use another software to reduce poly count e.g. Meshlab (free) or Hexagon (free) or 3DSMax (too expensive). Keeping uv mapping is possible only by the latter one. or divide the model into more pieces by a 3rd party model editor.