This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
AJAX is a concept. You will need to choose which library you want to use - jQuery, Dojo, etc. If you are in a big hurry, you likely want a book for that particular library rather than a general AJAX book that touches on everything. Especially if you are looking to call a specific widget rather than gain more understanding.