WINDOWS XP INSTALLATION

My WINDOWS XP professional was working fine and I have unallocated free disk space on my PC. So I formatted undivided disk space partition (150GB) to NTFS. Now I can see all the disk spaces like C: D: E: F:(CD-ROM). When I tried to install Windows XP using boot installation disk space get merged and showing like C: 131GB and Unformatted space 171GB. How this could was happen I have important data in D: Did all the data in D: Lost or possible to recover the same. When I did not formatted the C: drive how it will show the merged space.