Also before you do anything big (like installing something really big or important, or such as editing files), you should create a restore point.
To do this, open your control panel (this is on a Windows XP and the control panel is on category view not classic view) click on performance and maintainence, then on the left side bar in the "see also" box. Click on system restore. When it pops up, select "Create a restore point" then keep clicking next until a text box comes up, when it does, type in the name of the restore point (make sure you make it something that sticks out and that you can remeber. Don't put something like "Restore point 1")
after that click the next or finish button (can't remember at the moment) and it will save that point. If you need to ever use it, then when the system restore program pops select, "Restore computer to an earlier time" this will restore lost or changed information but you will not lose new information. (Like that school report that you worked for 2 weeks on
) After that just follow System Restore's instructions.