Do you want to carry around a fully customized operating system with portable applications? Do you have a netbook and want to test a different operating system? You may not have an optical drive and need to work with a different operating system. Then do this - boot the system from the USB stick!
Steps

Step 1. Make sure your BIOS version supports booting from USB stick

Step 2. Take a USB flash drive, the size of which is suitable for installing the operating system (4 - 8 GB)

Step 3. To install Windows XP on a USB flash drive, you will need fine-tuning and third-party software

Step 4. Windows users can install the following Linux distributions on a USB flash drive (directly in Windows)
- Ubuntu, Kubuntu and Xubuntu (since v8.10)
- Fedora (since v8)
- Knoppix (since v5.1)
- SLAX (since v6)
- PCLinuxOS MiniMe

Step 5. Non-Windows users need to use an optical drive and Live CD to install Linux on a USB stick
The following Linux distributions can be installed on a USB flash drive using a Live CD:
- Ubuntu, Kubuntu and Xubuntu (since v8.10)
- Knoppix (since v5.1)
- OpenSuse

6 Mac-on-Stick will let you download Mac OS Classic 7.01