Well.. after thinking about it and all those hours i've spent searching and all those stuff installed on my P3 1GHz, i decided to give up the try.
With all those ati software stuff, i noticed some strange behaviour on some game graphics, so i decided to keep my system simple. Unless there's a way to use that h/w decoder with installing only one app.
In Power DVD settings, there's a "enable hardware acceleration" check button.
When i check this, my cpu usage during dvd playback is around 35% and without having anything installed (no ati media center, no ati decoder or anything else.).
When i un-check this, cpu usage climbs up to 75%.
The same exactly was the behaviour with all those ati software stuff.
On the other hand, i find that on windows media player, in menu tools -> options -> performance -> advanced, the "Prefered decoder" settings are frozen... and still was that way after installing all ati software.
So no more framework, ati media center, windows media decoder, ati decoder, and many many more that finally proved to be completelly useless to me.
I now only have the latest version of drivers and i am happy!