There are different ways of doing this but if you don't back up think about doing it NOW.
Try one of the cloning utilities that will back up the whole of your mac to an external disk and make that disk bootable, our best of are:
1. CARBON COPY CLONER: (its FREE) Download version 3 now! (Tiger and Leopard) Clone, synchronize, backup. Schedule and forget it. Try it 'til you trust it. The key to a successful backup plan is to actually do the backups regularly. When left to a human, the task often gets tacked on to the end of a very long list of other things to do. When you eventually have a catastrophe, the data is simply gone. You know that feeling -- you just lost six years of family photos. Your kids being born, their first birthdays, their first everything. The answer to this is consistent and regular backups, placed on a schedule and handled automatically by your computer.
2.SUPERDUPER: (about £11) is the wildly acclaimed program that makes recovery painless, because it makes creating a fully bootable backup painless. Its incredibly clear, friendly interface is understandable, easy to use, and SuperDuper'sbuilt-in scheduler makes it trivial to back up automatically. And it runs beautifully on both Intel and Power PC Macs!SuperDuper's interface confirms all your actions in simple, clear language to ensure that the end result is exactly what you intended.
Then there are the seemingly more professional back up tools that have a degree of sophistication, reflected in the price.
3. RETROSPECT DESKTOP: (current version 6.1, also comes in workstation and server version for enterprise users)
Retrospect is specifically designed for use in small and midsize businesses, workgroups in large enterprises, and home and small offices. Retrospect provides complete protection for files, folders, and application settings on servers, desktops, and notebooks. Retrospect is easy to install and use, and it performs fast backups with 100% percent accurate restores. It utilizes automated technology to provide easy administration that allows small businesses and home users to protect their data without requiring extensive IT resources or unnecessary expenditures to train employees in complicated backup and restore procedures. Retrospect can be seen as complicated but our opinion has an efficent user interface, so beginners may struggle with having to write scripts for scheduled backups.
INTEGO PERSONAL BACKUP: Personal Backup's multiple backups protect all your files from unexpected problems. To keep all your files safe, you need different kinds of backups. Back up files to external disks or optical media, create bootable backups of your entire Mac, and synchronize files from one folder or volume to another.Back up to hard disks, CDs, DVDs, network volumes, iPods, iDisks...Fast and reliable restorationsCreate bootable backups of your startup volumeSynchronize folders and volumesCreate encrypted archivesSchedule automatic backupsCreate custom backup scripts
"Personal Backup X4 (Mac)" (Intego)
PROSOFT DATA BACKUP: From the people who bought you Data Rescue and the excellent Drive Genius (as used on Apples Guru desk instore) Data Backup 3 is a powerful utility that allows you to backup, restore and synchronize your valuable data with minimal effort. Whether you are a new computer user or a seasoned professional, Data Backup 3 offers you just the right amount of power, flexibility and ease-of-use to help you protect your files fast.
"Data Backup 3.0 (Mac)" (ProSoft Engineering)
Tri-BACKUP 4: Offers standard backup, restore and synchronization features, with a wide range of back-up options and flexible scheduling. However, Tri-Backup is let down by a confusing interface and offers only limited support for optical media- like CD and DVD. Costs around £25 and a trial mode for 30 days is also available.
BOUNCEBACK PRO: BounceBack is easy to use. It is the perfect solution for home users who do not want to waste time dealing with complicated, hard to use software. It's also perfect for business users who don't want to waste IT resources deploying a large, complicated backup solution. Although we found its interface a bit clunky and confusing at times, CMS who make this product have produced some great autobackup disks in their time.