If you don't already have a second hard drive you could get one and install linux on that. It would help if you know if it is IDE or SATA but it's easy enough to tell if you look inside. IDE drives have wide ribbons maybe 2" wide and SATA drive connectors are about 1/2" wide.

Hard drives are pretty cheap these days and if your existing drive is old you may not find out until it dies completely.

Linux installation routines are usually trouble free but I have, once, accidentally reformatted a Windows 7 drive without meaning to. Removing the Windows hard drive and installing linux on a fresh drive will guarentee you loose nothing. You can replace the Windows drive later and use F8 on boot up to choose which system to use.