The various versions of DOS and windows insist on being installed on the C: drive (a primary partition on your first disk). Other operating systems such as linux do not have this restriction and can be installed to any partition on any drive.
If you only have one hard disk drive in your computer then you will need to partition it to be able to install Linux (unless you get a version of Linux that will install in a windows partition - I do not recommend this). You can partition your hard drive using the DOS FDISK utility but this will wipe everything on your hard disk. A better solution is to use FIPS and Disk Druid which come with your Linux installation and can resize your existing partition without deleting the contents (but back up critical data first just in case). The best solution is to use a third party partitioning tool such as Partition Magic.
To select between operating systems at boot time you need to install a boot manager. Linux comes with one or more boot managers. The most common is LILO. When you install linux you install the boot manager. Then when you start up your computer the boot manager will allow you to select which operating system that you want to run.
Partition Magic supplies its own boot manager that provides a graphical menu to select which operating system to boot. To use Boot Magic (or any other third party boot manager) with Windows/Linux dual boot you need to install LILO in the Linux partition not in the Master Boot Record. Next you install Boot Magic to the Master Boot Record and edit your Boot Magic sessions to list both Windows and Linux.
This article written by Stephen Chapman, Felgall Pty Ltd.