Need help identifying cactus...San Pedro?

I just moved into a new place and there is a huge cactus in the front yard. My friends think that it is a San Pedro (Trichocereus pachanoi), but I am not sure. The plant is huge, it has one main trunk several branches which are not growing perfectly upright, more like 20 degrees off center. The main problem is that the branches seem to have grown in sections and when I see San Pedros they always seem to be one continuous smooth shape whereas this one is pinched in places. I know that San Pedro is quite a popular garden plant so it makes sense, but are there any other look alikes that might be duping my friends?
Are there any good places on the net to help me in trying to identify this plant?
Thanks.
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A picture of the plant would be most helpful.
There are many columnar cactus in cultivation, including many that are nearly without spines.
If the plant has nearly spineless blue-green stems with 6 to 8 rounded ribs and large nocturnal white flowers with silky dark hairs on the outside, it could be Echinopsis (Trichocereus) pachanoi or a related species.
If the stems have much narrower, almost wing-like, ribs and flowers without hairs, it is probably a Cereus.
There are also several other, less likely, possibilities.

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Sorry, it took a while to figure out how to get the pictures uploaded.
Here they are:
The first plant I am quite sure is a san pedro. Picture: http://img325.imageshack.us/my.php?image nb.jpg
The second one I am not sure about. Picture: http://img325.imageshack.us/my.php?image9lv.jpg Closeup: http://img325.imageshack.us/my.php?image ;0of.jpg
I have my suspicions, but can anyone identify these for sure?
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The first plant is Cereus hildmannianus, often misidentified as Cereus peruvianus in the trade. It is NOT San Pedro.
The second plant isn't a cactus. Its Euphorbia ingens, a plant with a toxic white sap.

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