Please ignore everything Jesse just said: He or she obviously knows nothing about OS X, and seems to know very little about computers in general. Or to put it more accurately, Jesse knows just enough to be dangerous, in that he or she has just given you a lot of false information and bad advice.
To answer your questions:
1) Will a Mac run Linux? Yes, absolutely. In fact, the Mac operating system, is based on Unix.
2) Will Linux allow a dual partition? Certainly! Regardless of whether you wind up buying a Mac or a Windows machine, I recommend Ubuntu Linux. It's installer will happily create a new Linux partition on your hard drive without forcing you do delete the data that's already on there.
3) How will a Mac laptop from between $600-1200 hold up with this theoretical dual partition? Any Mac, regardless of price, and regardless of whether it's a laptop or desktop, will work just fine with multiple partitions on its hard drive. I'm not sure what you mean by "hold up," but this certainly won't create any reliability issues, if that's what you're worried about. Nor will it hurt performance, as long as both partitions have at least ten percent free space so that virtual memory can function properly.
4) Would a computer preform better with just a single Linux / Windows partition? Nope.
5) What else should I need to consider before making this choice?
You should consider the fact that OS X includes Boot Camp, a utility which makes it insanely easy to install Windows and/or Linux on separate partitions on your hard drive. Jesse's advice about paying a technician to do this for you is just insane.
All you need to do is print out the easy-to-follow step-by-step instructions which Boot Camp will tell you to print out. Then, with your Windows or Linux install CD ready, simply launch Boot Camp and follow the instructions.
Apple's official party line is that to install Windows, you need a retail copy of Windows XP, service pack 2, or any more recent edition. The truth is that I was able to download and burn a hacked copy of XP SP3, and it installed with no problems whatsoever. I'm sure Boot Camp doesn't currently support Windows 7, but I'm equally sure that there will soon be a free update so that it does.
You should also use Boot Camp to install Linux. That process will probably be even simpler than the Windows install, in that there will be less for Boot Camp to do, since it won't need to install the Apple drivers that it installs with Windows.
Lastly, regarding your skepticism about whether Apple makes better laptops:
They do. Read Consumer Reports or any other publication that compiles customer satisfaction statistics. Apple laptop owners are consistently happier than owners of other brands, not only because the laptops themselves are much better, more reliable machines, but also because you get much better support from Apple after your purchase. You can waltz into any Apple Store and have a "Mac Genius" do things for you, for free, that the Geek Squad doesn't even know how to do.
Check consumerist.com for the straight dope on Dell, Best Buy, the Geek Squad, and other entities which make owning a Windows laptop pure Hell.