Point your browser at www.distrowatch.com
. Scroll down the page to see, on the right side, a list of the top 100 Linux distributions. Use the search (in the list at the top of the page) to search for liveCDs. Then choose one or more to download and burn to cd. Reboot with one in the drive and explore Linux without installing anything.
Study the tools for resizing/creating partitions. Your windows installations probably take up the entire drive, so you can use the tools in your chosen distro to examine your drives and decide where to make the free space for Linux (probably at the end of the drive). You will need a minimum of two partitions, swap and Linux.
The main thing is to use the liveCD version of a Linux distribution to become familiar with Linux before you install anything to the hard drive. You will probably be most interested in how well the distros detect and configure your hardware. This is the way to do it without commiting anything to disk.
If one distro doesn't work well enough, try another.
When you do install, it won't hurt windows unless you install in the windows partition. Things to do before you start messing with partitions:
1) defrag windows
2) make a backup of windows
3) make a windows boot floppy or boot cd because you may need it to boot into windows to repair the MBR of the hard drive if anything goes wrong when you install Linux.