Scale it down in MilkShape to approximately its original size before exporting. Poser meshes are very small (perhaps 5% of what would be considered a "normal" size in an application like MilkShape).

Also, if you want this to be a conforming clothing item, you'll need more than just the mesh. It'll have to be grouped into the corresponding body parts (chest and abdomen), and you'll have to create a .cr2 file to define the joint structure. Renderosity has tutorials on this subject.