The 42LH3000 has a 5ms response time - 5ms delay in your screen actioning a response to its video feed - resulting in motion blur. This will dramatically reduce when watching a better resolution i.e. HD. However, this is one for those who claim LCD is better than Plasma, they're simply not.
You could probably reduce the issue by changing your DVD video settings to output 'RGB' if connected with a scart lead, if its HDMI then that is the best you will get.