Sorry to have you unreplied since I'm now often online and very busy too. Anyways, check if you have done these things?
1.) Are you doing Overworld Tiles? Perhaps you are using Advance Map, right?
2.) If you know how to insert tiles, good. But, are you following the corresponding sizes of each image? I've forgotten the sizes but you can save a .bmp file to check or edit.
3.) After inserting tiles, you need to edit the tilemap as well in order to create tiles which is used in the gameplay (also editable in Advance Map thus I think this is the reason why yours are broken into tiny parts).
There are AM tutorials around on how to insert and replace tiles clearly and briefly.