Well, you want to find out what sort of PCI slot your main board has, and what wattage your power-supply/board permits.
-There's a slight chance you're running a 20 year old chassis that simply cannot run the latest hardware anymore (the silver-lining is there's shiny surplus stuff that'll probably still manage PS4 level graphics)

90% of the time, when it comes to graphics cards "if the chip fits, it ships" and there's probably software (drivers) to let it function properly out there someplace.... those linux folk are scary, though... And you're [i]kinda screwed[/i] if it's an Apple or Mac.

And lastly, desktop-tower PC master-race. When your rig is capable of being so large the air-ducts inside the case are big enough to lose a PS3 inside of... yeah... it has the case-capacity for utterly hilarious upgrades.
-Kinda like comparing a light pickup-truck to a racing ATV.

[youtube]https://www.youtube.com/watch?v=RRY1jrIDhvU[/youtube]

A bit of a tip is to have a hard-drive that'll function as a library of CDs instead of using CDs, as the read/write-speed is generally greater. Assuming of course doing so does not violate any EULAs (most of the time it won't unless you start renting out your hard-drive full of programs).

My approach was to buy a desktop from a pawn-shop for $200 and then clean and upgrade the hell out of it. Assuming you don't mind the system becoming [i]slightly obsolete[/i], it'll continue chugging for about 20 to 30 years with one or two comprehensive upgrade packages (current-gen graphics card to replace anything woefully obsolete, maxing out the RAM, using aging hard-drives as virtual-RAM etc) in its life.

And yes, I am that kind of guy to run a PC a five year old hard drive for storage, a ten year old one that came standard, and two twenties year old clunkers pulled from the junkyard running parallel as some emulation of a poor-sod's SSD.

[b]Oh, and the version of DirectX hardware acceleration your graphics card supports is probably going to be the first thing to brick your PC out of the latest games than actual performance.[/b]