This week's book giveaway is in the Spring forum. We're giving away four copies of Java Persistence with Spring Data and Hibernate and have Cătălin Tudose on-line! See this thread for details.
If the contents of the sdcard can be abstracted by a "File" object, I believe the interface that the File class exposes contains methods [something like File.delete()/File.rmdir()] that can help you here..