Very slow screen in MS Word 2007 on Vista?

There is a noticeable delay, of perhaps 1/2 second, between typing a word and seeing the word on the screen. If I hold a key down, the letters arrive on the screen in groups of 3 or 4 letters at a time separated by short pauses. It doesn't happen in Notepad, so it is presumably not the laptop's fault. What can be going wrong?