for an example of how not to do things, hnb is pretty good. it's a shame, because it looked like a handy, console based todo list with an xml backing. I don't mean to trash opensource work, but here's some constructive critisim
the code follows no known standard coding convention.
can help you there
whenever you use the magic cast operator in C, be really really sure you know what you are doing.
Node *pos=(Node *)data; ... return (int)pos;
The code does this at least a hundred times! Obviously some code that was copied from somewhere but renders the program usless on any 64 bit machine, where sizeof(int) != sizeof(pointer). This also says something about abstraction, since it does it so many times this really hints it should have been broken out.
If someone says "XML", think Python, Perl, Ruby ... anything but C