About a million years ago I remember you could go to the computer store and grab a motherboard, a CPU, maybe a coprocessor some RAM, etc and put together the computer of your (realistic) dreams for not a ton of money.
Is that still the case today? Or are you better served by just telling The Computer Guy what you want to do and let them recommend a pre-made system? Are CPUs and motherboards still reasonably interchangable or are things so finely tuned now that you have to pick an operating system and then find a board and CPU combination that will run it? And if you do throw something together, what are the odds of you being able to do it better than something already on the shelf at Best Buy for $250 less?