If you are installing a web design tool such as Dreamweaver be vary wary over making it your default editor for certain file types.
When I installed Dreamweaver it, by default, becomes the default editor for xml files. In previous versions of Windows this was not a problem. However, in Vista if you accept this you will no longer be able to view help or support pages.
If you've already screwed up help and support you can use this fix:
This registry edit will restore Help and Support in Windows Vista. Credit for this fix goes to Kristan - you can see the full thread on the Microsoft newsgroups.