In the Tutorials Forum there is an A* tutorial I wrote for Pathfinding in my Isometric game. I got it working quite nicely but never spent time on completing the game.

What I did for performance and optimisation is I did not do collision testing between objects but instead created a collision array covering the map. My tiles were about 32x64 bits (in diamond shape) but over this I created a logical array of 16x16 bit squares (quite a large array). Each object then knew how to inform the collision array where it was.

This means that if an object wants to move from one square to another it just checks the collision array and will immediatly know which (if any) object is in a square it wants to pass through. If an object could move it informed the collision array it was leaving a cell (removing the pointer from the collision array) and informed the collision array of its destination cell (once again adding its pointer intot he array).

Hope this helps a bit. I'm still not sure exactly what you want.