Dual-BootingThe easiest method is convert a PC having a single hard-drive into an exclusively Linux-based machine. This would necessitate losing everything on that hard-drive and installing Linux on it. Many people, however, own only one PC, and would like to continue using that PC as a Windows box. If you are of that type, you should consider setting up your (or a) PC as a "dual-boot" machine, capable of booting either into Windows or Linux.
There are two ways to do this, neither is very complicated. The simplest is if your PC has two hard-drives. Just move everything off the smaller-capacity drive onto the larger, then run the Linux installer, being careful to install Linux on the (now redundant) smaller-capacity drive. After the installation, you can use the PC's BIOS to select which drive to boot from.
The more complicated (but still easy) method is to provide a spare partition on a hard-drive onto which to install Linux. The main difficulty here is that most people, when installing Windows, do not provide multiple partitions; their hard-drive consists of a single, large partition, with Windows already installed on it. In that case, you'll have to create a new partition by shrinking the existing one. The trick is to do this without losing any of the data on the existing partition.
Partition Magic (and similar software) repartitions hard-drives without losing data (hopefully!) It rearranges the data on a partition so that it is clustered to "one side" of the partition, and then changes the partition definition table on the drive. The end result is that you have free space on your drive onto which you can install Linux. read more