Method 1. Try Getting ubuntu live cd. Boot it and you can use ubuntu without actually installing any OS. Go to your hard drive and use some external drive to save your data. I am not exactly sure whether you will be able to reach window partition with live cd but i dont see why not so give it a try. If it doesnt work try method 2 Method 2. Risk installing ubuntu trusting partition manager of ubuntu. But there is serious chance your data will get lost. If you dont want to take any risk but are willing to do some extra work, Method 3. Take your hard drive out of your computer and hook it into somebody elses computer or your extra computer and back up your data. Good luck