database column changes, 1.5x to 2.1

Is there a place where I can see a list of table column changes from wordpress 1.5.x to 2.1? Should I even bother to try to get WordPress 2.1 to understand a 1.5.x database (or to alter the 1.5.x db so that 2.1 is happy), or is this an hours long process, not worth pursuing? If the latter is true, can anyone recommend blogging software that tends not to strand old data as it changes?