For that you'll just need to purchase a cloning application such as Norton Ghost, Norton Save & Restore, or my personal preference, Acronis TrueImage. With any of those you can create a compressed copy of the entire hard drive on a set of CDs/DVDs, another hard drive, etc. from which you can restore your computer at any time. You can also make incremental backups over time to complement the initial backup.

Hope this helps,
John