Hi Tortellini, You could try "Using Software in Qualitative Research: A Step-by-Step Guide" by A. Lewins and C. Silver. The authors are based at the University of Surrey in Guildford and run really good courses introductory and advanced for NVivo - so if you can find the time/money to get there I recommend it. However, since the courses are good I imagine the book will be too!
Best of luck :-)