Hello There!
I've built a lot of computers and am an avid bargain hunter. If you want to build something you have a lot of options to consider. Due to the nature of emulation there are many options to consider.
What are your favorite games?
If you were to say Street fighter 2 and Mortal combat, you could get any computer out of craigslist for $200. Now if you were to say, house of the dead 2 or tekken 3, or any number of different 3d games, that is when it gets more complicated. Because of the fact that as the games get more complicated pcs have to be exponentially more powerful you have to take into consideration: If you want to play them all you will have to spend a lot of money.
What is your budget?
If you said under 200-300 you could get a full used machine running a athlon 64 3800 with a low level graphics card and 1gb of ddr400. This system will most likely run (just about) any rom based game and even a couple chd based games. Now a more versatile system will most likely run you about $600-$800. One thing to also think about when you are specing out your system is, you don't need to spend a lot on your graphics card a geforce 8400 is more then fine and are only about $40, compared to gamer cards like the geforce 8800gt (around $400) or the respective radeon series cards.
Now before I try to answer any variable, I just threw together a machine so that I can run most of the games in mame, some dreamcast games, zinc and various other emulators. This whole build minus a case cost me $600 (minus a case and optical drives (which I have left over).
Item numbers and pricing direct from Newegg.comMotherboardGIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX All Solid Capacitor Intel Motherboard
89.99ProcessorIntel Core 2 Duo E8400 Wolfdale 3.0GHz 6MB L2 Cache LGA 775 65W Dual-Core Processor
$239.99RamG.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-2GBNQ
$44.99Video CardMSI NX8400GS-TD256EH GeForce 8400GS 256MB 64-bit GDDR2 PCI Express x16 Video Card
$37.99Power supplyCOOLER MASTER eXtreme Power RP-550-PCAR ATX from factor 12V V2.01
550W Power Supply
$59.99Cpu Cooler A must for any custom machine, seriously why not?
ZALMAN CNPS9500 AT 2 Ball CPU Cooling Fan/Heatsink
42.99Hard DriveSeagate Barracuda 7200.10 ST3320820A 320GB 7200 RPM IDE Ultra ATA100 Hard Drive - OEM
74.99And all for a grand total of .....................
$590.93 + shipping
Hope I answered your question, also anyone else chime in, its fun bouncing specs around
