start drawing your tiles up in the left corner and work your way down. this would cause the character, if blitted behind the tree, to become entirly or partly covered by the tree.

Last year, back in my VB days, I worked on an isometric style rpg which used square ground tiles and free moving sprites (they werent attached to any tile). I also faced this problem and my solution was to exctract all possibly visible sprites from the master sprite array and add them to a smaller array. I then selection sorted this smaller array based on the y location of the object on screen. As you are probably aware, objects closer to the bottom of the screen come in front of further objects in an isometric view, so i just sorted them in such an order that the first item in the new array was rendered first. I found this method very slow, as you could imagine, when handling large numbers of sprites. I am now using the more common and significantly faster and easier method of linking the sprite to a particular tile and rendering it straight after that tile. altairs idea of making any sprite behind the player 1 was what i used untill i needed animated sprites - the npcs who roamed the level and also needed to be zordered.