Hey C! It's been a while, but I used to bodybuild, so I've used both free weights and the machines. Honestly, the machines are better at keeping your alignment correct so that you don't injure yourself while working out - Nautilus, etc.
Upper legs and back can be helped by a squat machine... but I prefer the one that you're laying reclined on a board and pushing up from there (you're facing the ceiling and your back is flat on the board/ramp). It keeps you from straining your lower back, which is easy to do otherwise.
Also, there should be someone at your gym that could show you a couple of the machines, and they shouldn't charge you anything to do so. It's part of what you pay for with your membership. Just ask at the front desk next time you're in and they should be more than happy to help you either right then, or the next time you come in if no one is available immediately.
Good luck! But if it hurts - STOP! It can be hard to do, but it's no supposed to be painful and sometimes people make that mistake and pull muscles. ALways STRETCH first!!!
