Your teacher cannot loan you an XP disk that belongs to the school. He could create serious trouble for the school by doing this. Schools can get volume licenses that allow a certain number of installations and come with a special license key that doesn't work with other XP offerings. There aren't legal public downloadable versions of XP at all. To get this to work, you're going to need your own legal copy of XP that's designed for the individual user. It can be a full retail copy or a less costly upgrade to a qualifying version you already own. It would be against forum policy for anyone here to help you with this. Sorry.
My teacher loaned me a windows XP boot disk, which he burned himself. I went home and used my 250gb HDD to downgrade from W7. Everything was going fine until I got to the product key, and it wouldn't work (I got the product key on this website called MSDNAA, which gives student free software with the product keys). Turns out that he gave me a school disk, which needs a school district product key. I turned off the PC by holding the power button. I downloaded XP from MSDNAA and since the ISO file had a .rar icon, I couldn't find it until today. I burned the disk with W7 burner, and popped it into the disk drive. The installation started off where it left off, all it needed to do was load up the disk. I got to the product key, and it didn't work, and it was the product key assigned to the XP I downloaded. I turned off the PC, and tried again, and now it won't recognize the CD as a bootable CD. I tried reburning the disk several times, still doesn't work, but it boots the school's disk just fine. My questions are:
1. How can I start the whole XP installation from scratch?
2. How can I make the PC recognize the CD as a bootable one?
3. Is it possible to put two HDDs on the same PC, install XP, and delete the partition containing XP on the 250GB HDD?