Will partitioning C Drive erase the windows on it?

NO and YES

C is actually a partition on your harddrive.

You can use utilities to shrink the C: partition and make a new partition on the space you freed up on the HD. This does NOT erase Windows on C:.

But it's also possible to mess with the C: partition which has the potential to damage or erase Windows.

And since 'partitioning C drive' is technically impossible, I'm not sure exactly what you're doing so I can't say what the exact consequences will be...

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Hard disks are partitioned to create drives.  You can't partition the C drive, because it IS a partition.

To make a new or blank hard disk usable, at least one partition must be created.  This is typically a "primary" partition as opposed to an "extended" partition.  The partition is then formatted, creating a file system, which makes the partition an accessible drive.

It is a common but very poor practise to allocate the entire hard disk capacity to a single partition, and it is often desirable to correct the situation.  To do so, one must resize the existing partition by making it smaller.  This results in the creation of unallocated space in which one or more additional partitions can be created.

This appears to be what you want to do.  If you want to convert the existing partition into two, MiniTool Partition Wizard has a shortcut function, Split Partition.  If you want more than two, shrink the existing partition, then use the Disk Management tool in Windows to create new partitions.

Although MiniTool Partition Wizard has built-in safeguards, total data loss is always a possibility.  To avoid disaster, create a backup image of the hard disk, which will permit restoring the original if needed.  I recommend Macrium Reflect Free Edition for the task.

http://www.macrium.com/reflectfree.aspx

Create a backup and store it on an externat drive or a sufficiently large USB flash drive.  Open the Other Tasks menu and use the Create Rescue Media feature to create a bootable Linux CD.  If the partition resize is unsuccessful and you cannot start Windows, boot from the rescue CD and restore the partition from the backup.

Normally you can make a partition (from Windows) leaving all the data on it intact if you know exacteley how it works and how to do it. ). When things go wrong in the 99.99% of the cases the problem is not the program but YOU!. I used Easeus Partition Master to create a new partition on Disk C: (Windows Starter in there) and install Windows 7 in partition D:. Anyway, when making changes to your disk drives is always a good idea backing up your system, especially if you're making changes to your primary drive.