How do I stop Ubuntu from hanging due to processes going into 'disk sleep'?

How do I stop Ubuntu from hanging due to processes going into 'disk sleep'?

I'm using Ubuntu 9.04 64 bit on an AMD. It regularly hangs for a few minutes at a time when some of the processes's CPU usage % goes into 'disk sleep'. During that time I can't start new programs and most of the programs on the desktop become unresponsive.