If you open the drawer and have a look inside you should see a small black rubber belt that's fitted between two wheels (one big, one small).
Wrap something around the drawer so that it can't close up fully.
Then using some a fine pair of tweezers gently remove the rubber belt, I usually pull it off of the smaller wheel first.
Now you can either clean the band, leave it in some freshly boiled water for a couple of minutes. Or replace the belt, I'm in the UK and used a 19mm drive belt bought from a electrical component shop, this is smaller and tighter than the original.
Refit the belt, try not to touch it too much and get it greasy. If you're fitting a new smaller belt be careful you don't let it ping off!
Pete
Pete Grimes, May 2008