Intellisense is built into 2005 for existing classes/methods etc.
So if you add a class/method it should just show up in intellisense - if your asking about how to get things like the additional information shown in tooltips etc. Then just prior to the method or class declaration type three single quotes '''
This will cause some xml to appear which you can enter the relevent information into - such as details on the method and its parameters. After you build the project, these will be reflected in the Intellisense. This feature is known as XML comments and was added in 2005.
Hope that helps a bit.
If your asking about getting