For those who don't have the installation diskettes or a CD which is bootable, you can create a set of diskettes by running the makeboot program located in the \BOOTDISK directory (for those with MSDN it will be under the OS directory). The format to run makeboot is:
where a: is the target floppy diskette drive.
More information can be found in the following Microsoft KB article:
How To Create Setup Boot Disks for Windows 2000
Please see the following Microsoft KB article for details on creating XP setup disks:
How to obtain Windows XP Setup disks for a floppy boot installation