UNetbootin allows for the installation of various Linux/BSD distributions to a partition or USB drive, so it's no different from a standard install, only it doesn't need a CD. It can create a dual-boot install, or replace the existing OS entirely.

Requirements

• Microsoft Windows 2000-Vista, or Linux, or a USB Drive.
• A broadband internet connection to download the distribution packages (unless installing from pre-downloaded media, see below)
• Spare hard drive space to install the OS in (varies depending on distribution)

Features
UNetbootin can install to your local hard disk or make a bootable liveUSB drive. It can also load floppy/hard disk images, or kernel/initrds, or (some) ISO (CD image) files, for installing other distributions.

More Info & Downloads:
http://unetbootin.sourceforge.net/