If the computer has a floppy drive, first find another XP computer, FULL format a floppy with the XP computer first of all (do not make a bootable floppy) and copy the (hidden) ntldr, ntdetect.com , and boot.ini files to the diskette.
If the computer has a standard boot.ini file it should look like one of these examples...
[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
OR...
[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Edition" /fastdetect
If you have installed the Recovery Console on your boot drive there will be an additional line...
C:\CMDCONS\BOOTSECT.DAT="Microsoft Windows Recovery Console" /cmdcons
Put the floppy with the three files in the A: drive and start the computer. If the drive has not failed completely it should find the drive for you. (Maybe... )