HD failed. replaced the drive, but how to re-install the original OS?

Hi,

I have a XP 15Z, an i7 laptop with a replaced disk drive (SSD - 500GB). Could someone point me to info on how to put the original OS back? I have the [Amin Note: Service Tag Edited per TOU policy], but support ended Sept, 2013. Any pointers?

Thanks in advance.

Tom