nope, nada, not possible - even with homebrew code. Believe me, I've tried and failed. The best you can do is get the Gameshark Media Player and watch movies stored on your computer using your ps2 with the ethernet adapter as the go-between for the data transfer.
the reason is because the hardware is designed to decode mpeg2 (dvd) - SVCD doesn't work either because of formatting issues. The Gameshark player works by making the ps2's hardware decode the video into a format the ps2 can understand.