How do backups work in VISTA?

Hello every body,
Could some one please briefly explain me how does backup work in VISTA and how often it is advisable to schedule the abckup on a “personal laptop”. While performing the backup procedure if the system requires for the cd from previous backups, does it overwrite old data or does it only perfoms an incremental backup? after 1 or 2 months can the 1st cd be considered obsolete?
Thank you very much for your great help!

Message was edited by: Jay Garmon