Enron was in the sale of electric power generation. They sold the production results of power generation companies. Power generation has nothing to do with the oil business.
Haliburton is in the oil exploration and production business. That is drilling oil wells and then getting the oil out of the ground and to the refineries.
However, most news reports conveniently state that Enron and Haliburton are both in the "energy business." I suppose you could say that this is accurate if you would also lump food into this equation because humans get energy from eating it.
I was amazed to see all of the strutting senators talking about Enron while including W's connection to "big oil" in their comments. I don't know about you, but I think that people who do that would lie to me if they had a chance. </sarcasm>