The best way is, to put your Hard disk in a external box (which u might have to buy), which then makes your HDD external and then save all your data to another computer. Then remove your laptop HDD from the box, put it in your laptop how it should be and then reformat the whole HDD. The process of saving stuff will take time and cost some money, again you only want to do this if your data is really very important, by important i mean like some important pictures/memories or some important documents, stuff you can never retrieve back. Once you save all your data you are now ready to install windows. That could be done two ways like i told earlier. For myself i use the vista installation disc not the recovery discs because they dont work for me lol. They require some skills in command prompt but i dont have those lol. So if you happen to have a recovery disc you might want to post another question, saying "how to run the recovery discs" because i dont know how that is done. But if you have a Vista disc then its no problem i can walk you all the steps needed to install the windows.