THANK!!!!
I ran Defraggler and after around an hour I noticed I lost 6.1GB (from 48gb free to 41.9!)!!! and it was only 30% done! So I Immediately stopped Defragmentation and searched online about it. It seemed that it has been happening to alot of people and the most common explanation was "System Restore Points", some suggested me to run a disk cleanup and after elaborating the search on that I found that the Built in Disk Cleanup (in vista) would >>>>DELETE ALL things on a hrad drive<<<< (due to some registry problem). Anyways I left that alone. [use CCleaner instead!! haha]
Then I found this post and I tried the thing where in Defragger click 'Action' (in top left) > 'Advance' > 'Check drive for errors' and to my relief I gained all my GBs back after 'Verifying Drive'!!! yay!!! Not only did I gain it back, i got an additional 1.6GB!!!!
So from 48GB Free, I ran Defraggler ...... after 30%defrag it became 41.9GB....stopped it.... ran dive check.... now have 49.6GB free.