What should I do?
more ram as suggested already ,after you do i would install sp3,
slow ,its only a Celeron CPU ,with 512 meg ram ,when is it slow ,what are you doing at the time ,what internet browser do you use ,include version ,you should try to fix the problem of the c:\ drive being almost full ,if it were mine i would remove the partition on C:\ and make it one and reformat and reinstall winxp