I used to use StruCAD files all teh time.
it mainly depends on what you want to do with them. search google for a strucad viewer and ask for the proper file, not just the dxf one. that will let you see the whole lot in 3D properly but wont let you edit it. if they have sent you the dxf it may (or may not) have been converted to 2D
as for 3D cad, again it kinda depends on what sector you are in. obviously if you are in structural steelwork then strucad might be the way to go.
i currently use Solid Edge and google sketchup, Solid Works is a very popular one and then you have autocad inventor and pro engineer (proE). they all work in pretty much the same way.