Member Rara Avis
The Windows update is both a good and annoying thing. There are important things you should absolutely download as soon as they are available. These are patches that Windows puts out after determining and addressing security issues with their software. You're best off downloading all the "Service Pack" updates.
The rest are miscellaneous things that are either helpful or completely useless (more of the latter, I'm afraid, than the former) and you can download them if and when you want. I don't believe (someone correct me if I'm wrong) that you can download anything from Windows' Update that will hurt your computer (at least anymore than Windows has already hurt it just by existing! )