I agree with Logesh, CADfix is an excellent tool for importing and fixing IGES files particularly the infamous ones that have been exported out of Catia. Several other FE vendors have adopted CADfix for their front end when importing various CAD formats because of its strengths in this field. However it is not cheap!
An alternative is Roshaz which can import IGES files (including Catia) and produce quality load balanced meshes which can either be solved using it's own solver or exported in Abaqus, Lusas or Nastran formats. It is very cost effective.
If you use Roshaz to mesh and export to Nastran do you lose associativity with surfaces. In other words do you just get nodes and elements to work with?
When you use Roshaz to create a run ready input deck for either Abaqus or Lusas, the results from these solvers can be automatically read back into Roshaz for display, i.e. a two way street. Unfortunately the Nastran link is only one way, there is only an export to Nastran option at present.
You will then need something like Nastran for Windows "File > Import > Analysis Model" to read the deck, run and display the results.
