Doubling or Quadrupling the RAM is one of the best and cheapest upgrade you can make. Esp if the machines are doing basic work. I have an 800Mhz PIII with 512 Mb RAM - runs much better than when it only have 128 mb.
Double the RAM on some of the machines and see how much better they run.
Maybe the P1 needs binning but the PIII 800 are fine. Just need more RAM.