If your computer has a Windows XP Product Key sticker on the outside of it, chances are you can get a replacement install CD or recovery CD from the computer's manufacturer (OEM) if you provide the serial number of the computer. Generally you pay for the license for Windows and not so much for the media, though the OEM may charge a few bucks for the CD itself and shipping. Note that if you are using a product key on a sticker on the computer, then you'll need an general OEM copy of a Windows CD (as opposed to a retail, MSDN, or TechNet copy).
If the computer cannot boot to safe mode, try choosing "safe mode with command prompt" as the boot option just to see if that loads.
You could also try the Last Known Good Configuration boot option.