I really can't believe you would want to put windows on that
Anyways, if you don't know that much about computers you get into bios by clicking the delete button while the system is booting up before linux loads. There should be something called boot sequence and to change it you either press the keypad's up and down keys or you hit enter and scroll to what you want, that really depends on the bios. f10 to save and exit. make sure it goes CDrom first and that on the list you have the hard drive otherwise windows won't boot once it's installed.
If you have an interest in linux you really do need to get the discs to the operating system.
note: if you use windows the most you won't use linux. I did that same thing and I eventuallly just deleted it because it went unused.I have lost all the data on my computer because of windows multiple times but I have never lost a single thing on a linux box, which now all of my computers are, and I love being able to know that when I'm typing up a paper I don't have to worry about saving it every half an hour. Windows is not a good, stable, operating system and if you now have two machines you should leave linux on that one and learn how to use it as a windows replacement, which is works wonderfully at. You will struggle with games most likely however.