However (and to my great annoyance, after many days of effort), I had a problem with the model's collision mesh. The collision mesh is, for those who don't know, a sort of metadata of the model. As you can imagine, it is processor-heavy for a PC to calculate and look for collisions everywhere. Also, it might be that the whole model isn't solid (imagine a window, through which, for game purposes, the player can go through) The collision mesh solves those problems, as it indicates where the model is solid (and thus where to look for collisions).
Now, I'm really no expert in moddeling -- far from it. So I use Google's (Trimble's now, I think) SketchUp 8. It's a fairly simple tool and serves its purpose well. Unfortunately, it's hardly game-ready modelling oriented. As such, when I exported the model, and re-imported it into Unity3D, the result was one hell of a mess. The ball would go through the model, and everything looked ugly. My lack of experience working on Unity didn't help, and I basically gave up. Seriously, I think it's beyond repair (and I'm definitely not going to do it all over again).
Not felling like putting all the work to waste, I'll just post a picture here, and the .skp file (SketchUp) available for download (under no license, if anyone can fix it, it's theirs. Seriously, I am so done with that model).