click here This is an excellent guide to a clean install of windows. It is the same method for formating an existing O/S and then installing fresh. If you have a read through and as you scroll down the page you will see some small blue panels on the left. Click on these and they will enlarge to show you on-screen guide.
Please post back if you need any more help with the installation and as to your other question, Your other partitions will be safe and not affected with the format of C: dive but as always make a backup of any folder/files that are important. j.