One of the things that made SharePoint developers lose sleep and hair over was the lack of intellisense support when working with the products XML files.
In WSS V3 and MOSS we will ship the corresponding XSDs. This is great news because you can use those XSDs to validate your XML files to make sure they are correctly formed etc...
Another nice side effect this has is the ability for Visual Studio to use these XSDs to provide you intellisense support when working on these files.
To get this going here is what I did.
You should now have intellisense working!
There might be other ways of doing this, but this is one method i have found to work for me. If anyone has another way they do it please comment!