To activate and use Backup, you must have a valid .Mac membership. Some features, such as backing up to CDs, DVDs, and hard drives, are not available to .Mac trial members.
I use a program to backup important financial and business files daily. Apple's Backup program does work very well, but the one big problem for me with Apple's Backup program, is that I like to check my backups about once a week to make sure everything was backed up. This isn't possible with Backup. You only have the option to restore from a backup, not to open it to check files.