You actually might want to check into a LiveCD like Knoppix
. It will allow you to save any work on your current hard drive partitions (without touching them) or on a USB drive, or any thing of your choice and it comes with many developmental applications already installed (including KDevelop).
Even tiny distributions like Damn Small Linux
(50 megs) include libraries to compile C code. So the size is as big or as small as you are willing to make it. Zero (LiveCD) to a few gigabytes, depending on what packages you have in mind. The cool thing about getting a LiveCD is that you can boot it up and use it on any computer you want (school, work, library, etc.) and load up your work with a floppy or thumb drive on-the-go, too.
* To answer your question directly, you can allocate free space on a given partition to install Linux without a problem.
* I would recommend two gigabytes, just to throw out a rough number, if you are *only* installing development packages and none of the other goodies. That is the amount I would use, whether it be wrong or right, I've never looked at the bare-minimum requirement for Linux.
Edited to include links.