Just follow either of the paths into the back of the facility. On the way, stop and use the terminal on the reception desk to learn about Archimedes and get markers for Hidden Valley and Black Mountain on your map.
Go through the corridors until you get to the little science station in back. Regardless of how you get inside, walk through the power plant. If you have 30 points in Science, you can point out that there’s obviously a problem and that you want to help out. If you have 35 points in Speech, you can lie and say that you’re with the NCR. If you have a half decent reputation with the NCR, you can just use that to pull rank and be let inside to help.
