I think I understand your move_to problem now. I had to invent that wheel for myself a while ago and the math was not trivial for me. I had to get my son to teach me new tricks. :) Even though they may not be the most elegant math solutions, they are reliable.
I uploaded this very basic demo: http://trollsouttaluckland.googlecode.com/files/sprite_test.py. Line 104 is the call to sprite's move_to. Line 106 is the code to swap the locations. The real work of move_to is done in the class and supporting functions. Cheers. Gumm
