Create a partition.
U could have several OS on different Partitions and each of them will work properly.
U could split C disk and if space it's not enough u could add from ur another disk.
If u don't have any utility to perform them i'd recommend Disk Director.
This is very reliable, easy-in-use and rather cheap software.
Besides it includes recovery feature (that would ercovery ur accidentally deleted partition).
have a look
http://www.acronis.com/homecomputing/products/diskdirector/