If you are going to go the route that @MinhMMK and @chrisplmr suggested, I would advise getting the G75. It tends to be a little cheaper, and if you are never going to move it around, the increase in weight makes zero difference. The G75 also has the more powerful GPU, if that is of any concern to you. I would counsel against a desktop because of moving it back home (if you go away to college). The G75 is definitely transportable, though I would not count it portable.
I forgot to make this next point in my previous post: Whatever you get as your main machine, make
certain that it has a 1080p screen. I can't tell you how many times it has made a huge difference in writing papers, doing CAD, or programming. Some of my classmates have little Macbook Pros, and they have to constantly scroll to see everything they are doing on their computers. I have to scroll about four times less often, because I have 35% more vertical pixels.
Your second computer should be a U36JC, or else a Toshiba Portege. Those computers are the same price as a Macbook air (and sometimes less), get better battery life (at least the Portege does), and
have full-voltage processors. The use of a real
🙂 CPU will make it run rings around the ultrabooks/Airs when doing anything intensive. Sometimes, you will have to do intensive tasks away from your main computer, so having a sidekick that has some grunt is definitely worth it. The Portege is about 3 pounds, which is plenty light for moving around.