first if all fragment is making pieces if u do that the computer will go slow.so we defragment .
what u need is making additional partitions .
to help u in that we need to know your operating system (eg. - windows xp , windows 7 , windows vista .
if u have windows xp , then u need to re install windows ( i dont think any program exists to do it without re installing )
if u have windows vista or windows 7 , then let us know , we will give u step by step guide