not a big problem. go to your desktop and right click on "my computer" then select manage
into manage window select disk manager on the left hand side.
you will find the unallocated space on the right hand side having black color.
right click on it and select create new partition and then follow the steps make it whole in one first.
then if you wish to create more partition from it you can do it.
but it is a kind of tricky part. i suggest you to use some partition manager software for it.