Oh my god.... this is awesome! Really good job!
Now the game seems a real game
About de transparency, if I undestood you, you're saying that, if you make the graphics more big than the original ones it appear chopped, right?
The graphics sizes are stored in the file graphics.ini, in there you can specify, for every item, where it starts in the tileset and it's size. Actually, the tileset it's divided into 64x32 cells (top-left its 0,0 and bottom-right it's 7,15). These are the default sizes for a tile.
Example:
[tree]TILE_X = 0
[tree]TILE_Y = 0
[tree]TILE_HEIGHT = 64
[tree]COLOR_MINIMAP = DARK_GREENThis means that the "item" 'tree' begins in the 0,0 cell and has an height of 64 (instead of the default 32).
About de "border sprites", I discarded it at the beginning of development because the combination of different tiles was enormous (ex: a grass tile with water on north and a stone on sout-west and lava on the south, ....). But maybe I will implement it using some OpenGL blending functions. I still have to think about it.
Supermalparit
PS: I will test that tileset right now, I like it a lot. I don't know if I said to you before but... good job!