A:
Every computer has some form of audio jack in the rear. People commonly call a 1/8 inch jack a headphone jack, but that's just common parlance. It's used for many things.
If, in some indescribably unlikely circumstance, you don't have one, you could simply pick up an adapter for a few bucks, but I am an advocate of sound cards.
I personally use an Asus Xonar D2X. Those are hard to find, though. Anything from the Asus line is good. They weren't messing around when they designed their sound cards.
Creative is another obvious choice, but I haven't been back to them recently. They had a period when their drivers were a bit of a pain, but I've been told that's been sorted for several years now.
With either company, you'll be good. Neither of them make a single product that isn't worth buying, though I'd search in the upper end of their ranges, given the quality of the speakers you're considering.