Koko,
It looks like a Stenocereus, I'm not sure of the species. Check out DT's site: http://www.deserttropicals.com/ to get you started.
Dan
Lincoln, NE USDA Zone 5

Here is a link that might be useful: Desert tropical

hi dan,

thank you for the link, it´s very useful.

have you seen the other pics of this cactus? (there are two more posts from me)
i am confused. as said, i bought this cactus believing it is Echinopsis pachanoi... but after seeing pics online i wasn´t sure anymore. E. pachanoi doesn´t ussually have such big thorns or?

koko

Maybe it's a Trichocereus (Echinopsis) Peruviana? They are supposed to be very similar to Pachanoi but with longer spines, and the rib/spine counts seem to match yours. I've got a Pachanoi myself with the shorter spines you see in most pictures, but I think there are many variations.

Fredrik

Here is a link that might be useful: Peruvian Torch cactus