Firstly, is jumping really involved? Like most RPGs, DKS occasionally suffers from the 'slightly too high barrier that you can't pass' syndrome - e.g.: barriers that you could obviously climb over in real life, but which are impassable in the game, therefore forcing you to find another solution...

Otherwise, you'll need to supply some more details. Can you let us know which areas/jumps are causing problems?

Maybe the video walkthrough might help - you can find them on this thread:

http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Main=28060&Number=442427

Good luck!