WSPBuilder is a tool for building web solution (WSP) files to deploy out to a SharePoint farm. It is free, open source, and available on CodePlex here: http://www.codeplex.com/wspbuilder. It is a tool that, in my opinion, every SharePoint developer should
SPWeb.EnsureUser
Suppose you need to perform some actions on a SharePoint user such as role assignment, but you are unsure if the user exists within the site you are currently working with. One solution, which I have always used, is to