Well PIII, 600MHZ computer just barely meets min requirements of running multimedia apps.
So if any other bottlenecks due to poor maintenance of computer will hurt performance.
Well macrovision is copy-protection mechanism when playing commercial DVDs. If using old windows media player, likely won't be able to play DVDs anyway.
K-lite codec packs includes MPEG decoder as well as other packs. However, I suggest you stick with 1 or 2 players and only install what you need. You got too much unneeded codecs/players already that may add conflicts. FFDshow along with MPC (directshow player) will play most formats.