1. OK, you could "thin down" the Windows XP with SP3 CD files or ISO with "nLite" so it can run faster than SP2 or SP1....
2. Or even a lightened down Windows 7 can run faster than Windows XP SP3 depending on your CPU and RAM.
3. And if if you use the computer for internet browsing, e-mails, even watch videos, but nothing heavier, a Light Linux distro may be your best option.