I think a lot depends on whether your brother is willing to actually learn how to use a computer properly. If it's just his personality to "push buttons until something happens" and he doesn't want to actually learn the system, then it really doesn't matter if he's on a Mac or a Windows machine--or a manual typewriter. It's just not going to work as he wants.

So, this is probably the first question to answer. If he's not willing to learn, then a new computer isn't going to help, unless his attitude is because his cheap eMachines computer is such a piece of junk that it doesn't work properly and THAT is what makes him just push buttons until it does something.

But if he's willing to learn, Macs are great. I use a Mac as my main personal and work computer, although I still use Windows daily for work, too. Depending on what your brother uses a computer for, it really may not make much difference whether he uses a Mac or Windows. Using a mouse and starting programs, dragging files around, etc. are conceptually pretty similar, although there are differences that can be a bit strange at first when learning a new system.

You can probably get a better deal on a Windows machine than a Mac, but then again, I feel like I see people using their Macs much longer than for Windows machines, so over the long haul, the Mac may be cheaper.