This is only happening after going to chapter 2, for cut-scenes with nudity like with Succubus or the elf girl(not the dialogues). Otherwise the game is running fine with no other problem so far. I tried on every graphics settings and installing latest nVidia drivers, nothing helped. I copied my save games my friends computer and for him the clips works fine. Advanced thanks to any helps.
My spec:
Intel Core 2 duo 2.53 GHz
4 GB ddr2 RAM
1.5 TB HDD
Gforce 9600GT card

Are you actually given a choice via dialogues for the type of the reward you want?
Furthermore are you running GOG edition of the Witcher 2?
Also what version is your friend running?

Yes, I am given reward choice via dialogues, and we are both using GOG edition version 1.3.5

Have you tried lowering the game details to see if the cut-scene will play appropriately?
Furthermore how much difference is there between your and your friend's PC?

Since you are saying its these two cutscenes automatically skipping, I assume other cut scenes ARE playing?

Sounds to me like censorship. I know the australian version originally (does it still?) skipped a few sex scenes on the principle of "sex as a reward = bad". However as I understand, in the censored version you don't even get the convo options =S

Yeah, the censorship part is skipping the option in conversations and not skipping cut-scenes. So I am wondering what is the difference between his PC and his friend's PC and if the cut-scene plays at a lower settings...

Yeah they are always a bit hard with their censorship.
Anyway, I fixed it, turned out some files were not copied during installation[anti-virus blocking?]. I reinstalled the game with anti-virus stopped and now the cut scenes work. Thanks for all your help :]

Haha... that's kind of funny.

You sure that was anti virus and not parental control software?

=P

Oh noes i can't view teh nekid ladees!