How to fix a missing pci.sys from an xp?

i was using my averatec laptop running windows xp, when all of a sudden it shut down, because of overheat, i thought, since i was using it on my carpet and it wasn't connected to the internet. I think i was using photoshop and a multi track, and that may have overloaded the system or something, but the bottom line is that it shut down. I thought, "NO!! YOU SODDING COMPUTER I DIDN'T SAVE MY WORK!" and i let it 'rest' and tried it the next morning, but when it (didn't) boot up and showed the message "It appears that the file c:/WINDOWS/(something)/pci.sys is either missing or corrupt" and it (that sodding dollop of a computer) asked for the xp installation cd. Now, that wouldn't be a downer for me, if only i DID have that cd! You see, since the laptop is not mine, I borrowed it from my 'aunt' and she had lost that cd, im stuck, and the worst part is, SHE WANTS IT BACK! so please i desperately need someone to tell me what to do without having to buy xp again or updating to win vista or 7or buying anything at all. Also, when i boot it normally it just keeps on restarting with no stop, and if i try safe mode or anything loike that, that little message will come up and the computer will start all over again, so i need you to help me as soon, acqurately, and as free ($) as possible. Thank you and good night