To create a bootable USB drive, you need to Download the USB_MultiBoot program (the latest version is 10). You can find it using a search engine; I won't provide a link. Then:
1) Extract the downloaded archive and go to the USB_MultiBoot_XX folder (XX is the script version number);
2) Run USB_MultiBoot_XX.cmd; a window will open. Press any key;
3) You will be given the option to choose a method for formatting the USB drive. Enter P and press Enter. In the window, don't touch anything; press start, then Yes as many times as it asks. The window will reappear; press Close.
4) Now, a field for input will appear in the window:
a) Press 1, then Enter. A window will appear with a selection of Windows XP distributions. Choose the location where you have it. Another window will appear; press Cancel. If you encounter Yes/No combinations, press Yes.
b) Now, press 2, then Enter. In the window with the selection, choose your USB flash drive.
c) Now, press 3, then Enter. After that, press Yes everywhere.
The bootable USB drive is ready. Now, you can install Windows on a system without a CD/DVD-ROM.
Bootable USB drive menu:
Item 1 starts the installation.
Item 2 continues the installation from hard drive (partition) 1.
Item 3 continues the installation if the Windows files were extracted to the second hard drive (partition).
Item 4 is selected after the system is installed. In the list that opens, select the last 16th item; the system will boot. Now, go to the C: drive (system drive). You need boot.ini, which you open with Notepad. Replace rdisk(1) with rdisk(0). The system should now boot without the USB drive!