if you upgraded then you will have a folder called windows.old
However, most people do a complete re-install, which wipes the HDD and destroies all files which were on the computer previously.
In short, if you cannot find the folder, then it is lost and gone forever. As it has been said by others; If you do not keep 3 copies of your files then you do not care about them. Backup, keep multiple copies, and copy your backups on multiple mediums.