Which OS are you running? ForWindows 7, it's pretty simple.
1) Connect an external drive to your system. An image backup copies everything in the OS partition ( C: drive), so you need a drive that's as large as the OS partition is.
2) Start -> All Programs -> Maintenance -> Backup and Restore
3) Click "Create a System Image" to back up the OS and recovery partitions to the external disk drive.
But doing this is of no use if you don't have a system repair disc.
4) Insert a blank DVD into your DVD writer and click "Create a System Repair Disk". This will burn a bootable DVD that you can use to restore your system. You need this because if your OS drive dies then you no longer have a working copy of Windows 7 you can use to restore the backup with. You only need to burn this once - you can use the same DVD to restore whichever image backups you make in step (3) above.
For running it on any other system, connect the external HD to it. Set the bios to boot from CD/DVD & restore the OS.
4) Use the program on the "System Repair" DVD to restore the image backup.