Sorry if this has been asked before, but I couldn't find anything on it (or maybe I'm not using the right search terms).

Messy as in:

1) You can see all the cuts; pieces you stack atop each other has a moving reflection sort of thing when you zoom in/move the camera. For example, if I made a table and the legs went a bit inside the tabletop, you could see that via weird reflection-like things even when the pieces aren't transparent.

2) While in Wings 3D I made it all nice and hard (set the 'hardness' to 'hard' on the edges command--selected smooth shade too to test how it looks), and it looked that way in SimPE too. When it got into the game, it looked horrible. Besides the visible interlinking parts, it looked 'soft' and really ugly. Like a rejected fluffy desk.

I'd give a screenshot but I'm in midst of trying to find out which object has crashed my game.

How can I fix this?

yeyavailability,
your first problem sounds like you got the normals inside out,
meaning that your texture is on the 'inside', instead of on the outside of your mesh, where it should be
i don't actually know how to fix that in Wings3d, but try and see if you can 'flip' them
that might fix both your problems, actually

Go into Object mode, right click on the object, then select "Invert".

Is it supposed to look incredibly thin and weird when I invert it? It looks completely wrong, to say the least.

mk, maybe that's not it then.
pics might help us figure it out easier, though