OK - information for those with similar problems. i moved my WIN7 to other physical HDD (made a partition clone with Norton Ghost from Hiren Boot CD) and problem was gone. So: if operating system was on Seagate 7200.11 1.5Tb and was playing moves from same HDD - freezes was regular - once every 15-3...
got my old Radeon x1600 out of the box - still the same. On one of the freezes got distracted with a phone call and accidentally found out that - in ~3-4min system comes back to life as nothing ever happened. This problem is exactly the same for every video player i tried - only frequency of problem...
I'm lost now :( As latest pre-release version also had same problem i started to use Winamp for movies :( and guess what!!! Same problem!! It took me week to get it. With VLC it happens much faster. Membest , prim95 test indicated no problems, setting up power levels in BIOS (from "auto") ...