Well generally they cant! There is a chip you can buy (but its rarely seen now) that will allow vcd/svcd to be played in a ps2! You can make a disk with a movie on it and play it in your ps2 but it would only allow a few minutes, and would only then work in a ps2. There is a divx player you can download for the ps2 aswell but it also requires a modchip!
thanx for that, interesting about divx & ps2 does fitting a mod chip require opening the box & soldering?