Use the Bootable CD of windows XP and try to repair. Repair option will not let you loose any of your data and what ever the file system which are missing under your operating system will be restored.
But if you try to re-install the OS then all your data will be lost and you have employee
data recovery software to get back your data.
I did a stupid mistake some time back and for that I have to pay the price of $99 for getting Stellar Phoenix Windows Data Recovery Software.
Resultant I got back all of my data.