Hmm, thats weird...
Have you got the latest version? Windows Movie Maker 2.0? Its simply an update, if you have XP installed.
If you haven't got it, download it from the Microsoft website, or find it on the web
Hmm... actually, the link goes straight to the Microsoft download site, and that doesn't work anymore. It seems they've made it only possible to install through Microsoft Update.
Still worth a go, as it does improve it, and may fix your problem.