Right... You know the tool called Block Editor in Advance Map? You use that. You save the tileset in the pallette you want and open what you saved in Paint. You add the tiles you want by replacing or putting it into blank space. Take note that each tile is made of 8x8 Blocks. Recolour your new tiles into the colours of the others as you see fit. Go into Block Editor and go to Load Tileset. It should be loaded. The rest is easy, and I cant really explain it well. Look at a tut.
:O Wierd how there different time zones. Is the PC going slow with you now? I am wondering if it is just my computer... Keeps showing up "Database Error"...