You can get a XP CD from someone you know as long as you have a legit license for it. When you purchase Windows, the CDs are all the same - it's the license that is different and really matters. Assuming you purchased you PC new from some manufacturer (Dell, Gateway, etc), you should have a legit XP license. Look for a sticker on your case (usually in the back) that has the Windows key on it. That's what you'll need to reinstall Windows.
Depending on how old your PC is and where you got it, you might also have restore options. Usually a newer PC will not come with a CD but will have a restore partition. I guess since you said you had a CD then you probably don't have a restore partition, but I thought I'd throw that out there anyway.