Reformat w/o Windows Installation disk

[tom1590]

Story:
I built this PC about 4-5 years ago and have neglected it (i know, it'll never happen again), I've got a new laptop on the way and I was going to give this one to my father. I do NOT have my windows XP installation disk that I used initially for this comp. However, my school allows me to d/l a free copy of Windows XP.
Problem:
How do I reformat my computer w/o the initial installation disk, is there a way for me to d/l the XP OS from my school and put it onto a CD? If so, what type of file do I burn it as and the size of the OS file is at least 500 MB. I can't just burn it as an ISO file to a normal CD-R disc can I? Seems too easy, (I'm not very sure how an ISO file works) I'm unsure what type of file the windows installation CD is. Any help would be greatly appreciated.
-This computer does not have a backup.
P.S.: I know this sucker can be saved, just needs a little lovin'.
-Tom

[glc]

I can't just burn it as an ISO file to a normal CD-R disc can I?

It very likely is that simple. Very good chance that's exactly what the download is - an iso file.