You computer has some small slots for different types of digital camera memory cards, right? That's why you see:
CompactFlash (G:)
MS/MS Pro(I:)
SD/MMC (F:)
Smart Media/xD(H:)
I don't know whether you know that you could buy blank DVD disks at any office supply store and backup, or "burn", files to the DVD. Your DVD drive may also be able to burn to CDs, not only DVDs.
Your main issue seems to be that you want to backup files to some location other than drive C, and that's good thinking. Your C drive has plenty of free space. One or more additional partitions could be added and that/those partition(s) could be used for short-term backup. But, since hard drives are mechanical devices and can fail, backing up important files, photos, etc. to some external media such as CD, DVD, flash drive, or an external hard drive is much better and safer than keeping everything on your internal hard drive.
Actually, you could create backup files on C; it's just better file management if you can separate backup copies of files somewhere other than C. You could create a folder named Backups or whatever or use it for backed up files. But, again, this still leaves your important files vulnerable to hard drive failure or risk if your system gets infected with viruses and other malware.
If you still want partition drive C to have one or more separate, additional partitions, Windows Vista has a feature called Drive Shrink which can be used to do that. For information on this, see:
How to Shrink and Extend NTFS Volumes in Windows Vista