I have a Nokia N97 mini. I love it! For everything it does, it does most of it great. Now, here is my issue. I live in China. I would like to be able to copy the map of my city out of my phone into my computer, modify the map (basically, put colored lines on the map for selected bus routes using MS Paint all over the map) and then reload it into my phone. Does anyone know of any way to do this?

As an alternative, could I do this with an alternate GPS mapping software such as Garmin? or others?