Hi,
Installing a new operating system will always result loss of some data , its always better to make backup for it.
You could also read:
Installing a new operating system can overwrite at least 1 GB. All the files that were once located on this area of the drive are irretrievably lost. The directories entries (FAT) and MFT entries (NTFS) located there will be lost, leaving only files without reference ("lost file"), that had been allocated in undamaged areas beyond the 1 GB area.
In FAT this will also destroy the FATs, thus causing the fragmentation problem. All you possibly can recover will come from the not overwritten area.
Hopefully this helps till experts give their advice.