It is very easy and simple to make a boot able usb. Normally all notebooks have the option in the BIOS to boot from USB. Many other mother boards like intel 865, 915, 965 etc has also option to boot from USB device. So it is very simple and easy way to install XP on your computer.
Install it on your computer and then start this program. It will show two different paths. In first browse option you will select windows XP disk and in second browse option, select your Pen drive/USB. Click next to proceed. It will copy all files of windows xp from CD to USB. Now click finish. It is complete.
Now you can use this USB for installation of windows. Enjoy