My computer has audio jack at back panel and on front panel - i use to connect my headphones to front one - then i listen music (i.e. through winamp) i can hear it from both my headphones and my speakers (that are connected to back panel)

My question is: can i separate sounds? like i want to listen to music on my headphones (on front panel) and at the same time there would be playing movie and using back panel audio jack.

I don't think you can, you could try playing one with one program through the speakers on a sound card and another in another program through the motherboard. I can not see it working. I have never tried and I can see no use in trying. I have accidentally, had two programs with audio running at once through the same output but not through two different outlets.
I know you have two ears, but why would you want to listen to music through your head phones and have a video play through your speakers at the same time?

it is not like it i would like with one ear listen to music and with another listen/watch movie,

my computer have 2 monitors attached and the whole point is i would like to run movie on my secondary monitor for my brother while continuing my work with my main (while listening music) or watching youtube etc ..etc

my main interest is not like the usability but possibility

Hi again, as I said, I don't think it is possible. You could do both without audio on one.