A "Hackintosh" is any non-Apple computer that runs Apple's OS X operating system. This is advantageous to actually purchasing an Apple computer because it's cheaper and more customizable. Is this legal? To be honest, I have no idea. However, to avoid tempting any Apple lawyers that happen to also browse Facepunch, this is for educational purposes only. Yeah.
If you have the right hardware, it's pretty simple to install OS X on your computer. If you don't (like me), it can be extremely confusing and frustrating. I only reccomend attempting this if you have a lot of free time, and only if you really want to run OS X. I would also reccomend you have a strong understanding of computer hardware before you attempt this. In the end, as frustrating as it can be, I think it's worth it. It definitely saves you a lot of money, and using OS X is definitely a unique experience.
If you're planning on installing OS X on your current machine, keep in mind that there's a decent chance that OS X won't work entirely with it, especially if you have an AMD processor. However, anything is possible! If you're looking into purchasing a new computer just for OS X, or want to know if your current hardware will work with it, have a look at the OSx86 Wiki Hardware Compatibility List. In general, it's a good idea to stick to Intel processors, Gigabyte motherboards, and AMD/ATi video cards.
Once you're sure that OS X will work on your hardware, you're ready to install OS X. If you don't already have OS X Snow Leopard, you can purchase it here. It's only $30! Once you have the OS X Snow Leopard Installation DVD, you'll need a "boot CD" to install it on your system. You need this because non-Apple computers can't just boot up any OS X Installation DVD like you would do to install another OS. Common boot CD's include iBoot and Nawcom's ModCD.
Once you have OS X installed, you'll more than likely need to install kexts for your system. "Kext" is short for "kernel extension", and is the equivalent of a driver in Windows. You might need a kext for things like your video card, USB ports, audio, or even for system-critical parts like SATA controllers. You might even use a modified DSDT - a Differentiated System Description Table. In general, a modified DSDT can help you get your hardware working with OS X the same way kexts can. Kexts, however, are easier to find and use, and there's no need to modify your DSDT. However, if you can find a DSDT for your particular build, it's a quick way to get your system working perfectly in a short time.
There's a lot to getting OS X running, and I've only covered the basics. I'll try to include as many resources as possible about the creation and configuration of a Hackintosh. If you haven't tried this yet, and you feel capable, I'd absolutely reccommend it. It's a very interesting experience, and if you can get OS X working, it's a very nice change from Windows!
The OSx86 Project - Probably the largest resource of information regarding making a Hackintosh.
OSx86 Project Installation Guides - A very large collection of various OS X installation guides for various hardware.
tonymacx86 Forum - A Hackintosh forum with a large and active community. However, they provide support for Intel processors only.
Kakewalk - An extremely easy way to install OS X, but only on their small list of supported hardware.
OSx86.net - Probably the largest source of downloads for your Hackintosh, including Kexts, boot CD's, and more.
UniBeast - The most successful method I know of for installing OS X on almost any Intel-based computer. I definitely recommend this!
This informative graph found on Google Image Search describes the experience pretty well.
Post your questions, experiences with a Hackintosh, or the specs of your current Hackintosh builds!
Mac OS X Mountain Lion 10.8
Cooler Master HAF 912
RAIDMAX 700W PSU
MSI Nvidia GTX 460 768MB
4GB (2x2GB) DDR3-1333
I have no idea how to make a megathread