How to take an image of an hard drive partition

You didn't tell us what operating system you're running. In Windows 7 there is a built in imaging tool. If you're not running 7 there's plenty of third party tools for this, booth free and payed. A good free one is Macrium Reflect. You don't have to reboot when doing the image, only when restoring it, in that case you use a restore CD which you can use the imaging software to create.

I would personally recommend using Symantec Ghost Solution Suite 2.5...it does cost a few bucks but it is well worth it.

If you are technically inclined then I would say use dd (*nix command). Just BE SURE that your if and of are right :). This would be an example:

dd if=/dev/sdc1 of=/home/user/image.img

dd would make a sector by sector copy of the hard drive (or partition in the example).