OBJ is my usual way to get objects around. 2.49 did read many formats, but most of them are not in 2.55 yet. OBJ import seems to work fine, with this version I have imported from ViaCAD, Shade, Wings3D, Silo, umm... too may to list. ;-)

There's multitude of reason to see "nothing". Usual problem is that the modeler makes things, say, thousand times bigger than Blender's scale. What you see is insides of the object, that may look quite gray... Or then again, objects is so tiny that you see nothing. Hit 'S' key and see what happens...

Btw that image is quick random modeling in Sketchup 8 Pro, some boolean / solid tools stuff. Imported as OBJ, then curved surfaces smoothed a bit.