PROBLEM INSTALIN WIN XP PRO ON SONY VAIO VGN FZ 19 VN

i could use information on installing win xp on my vaio VGN – FZ 19 VN
i have purchased an external usb flopy (its a nec)and followed instructions (pressing f6 at the begining of windows inst. as sony describes in the site)the installation recognizes the flopy and the drivers, lets me format my hdd but when the format finishes and windows check my drive wright before windows start copying files on c: i get the mesage “put matrix storage driver in drive a and press enter” althuogh my usb flopy remain conected and the discet in its place. It seems that the computer dosent recognize the usb drive any more.
would apreatiate it very much if you could help.
sorry about my english.