What end result are you looking for? A full feature tree that will be editable? If so you will need to import it as a part and use featureworks to try to get an editable history. I have found the interactive one works pretty well for me after alittle tinkering around. Their are also options for importing IGES files in system options.
most likely the iges only contains wireframe and no surface data.
so who did you get the file from and what software created the iges?
sometime the person creating the iges needs to flavor it to work in other systems or they need to select what they want included.
I would call them and ask if they could send you other types as well, step, sat, parasolids and se if they work better.