I have had this problem with my Bosch dishwasher and have fixed it. I searched around and an appliance engineer on the web laid it on the line - he said that the crud we find on our dishes and glasses especially noticeable on the top rack can only come from broken down food debris. There are four things to do - I did (do) them all and it's all nice and clean now.
1) Rinse off as much debris from the dishes before loading the machine (we seldom did this) Weetabix, mashed potato and egg are allegedly some of the worst offenders.
2) Use a good quality Rinse Aid and turn the dispenser adjuster up a bit (we used rubbish cheap rinse aid and not that often) The real purpose of this stuff is to break down water tension (not to make the dishes shiny) to allow the crockery to drain better. If droplets of water with crud in them remain on the crockery to dry in the steam-heat any dirt in the droplets gets baked on hard - especially noticable on glasses.
3) Clean out the filters and run a load with a couple of cleaning tablets now and again.
4) Pay some attention to loading the machine so that all the crockery gets a good splashing
You might try this first before attacking the pump which will probably be underneath near the floor.
I think there's two pumps - one to circulate the water and another for draining - here's a picture...
http://image42.webshots.com/42/1/91/17/366919117wvLVhf_ph.jpg
Good luck...
Peccavi
March 2009