This gives a summary of what Enterprise 2.0 / Web 2.0 means for large companies, and give some broad reasons why your first initiative will probably fail. It covers how you might fail because of the wrong technology, or the wrong culture.
However, because of the very nature of Enterprise 2.0, your only hope for success is to lose your fear of failure. Instead, expect failure: try, fail, learn, try again.
Ultimately, in a Web 2.0 world, finding genuine value is more about experimentation than it is about following a cookbook recipe.