I tried running these games on my i3 laptop which just has crappy on-board graphics and they ran but were unplayable because of how slow they were (Type X games were able to play perfectly fine)
So are you asking about the Taito Type X games or the Steam/PC versions of them?
The Taito Type X games are less demanding, but as far as I know the 2 player version of SSFIV hasn't surfaced.
If you want fighters, don't skimp on the processor or video card or you'll miss out on the ones running on Demul.
(Guilty Gear, Dead or Alive Millenium, KOF Maximum Impact)
IMO:
For the processor, 3.2Ghz or faster
For the Nvidia GPU, 800, 80 series or higher (i.e. 8800 for old generation, 480, 680, 780 for current generation)
You might get away with a 60 series of the newer generation.
I'm getting by with budget setup of outdated parts - 3.4Ghz Athlon X3 & 9800GT.
I have to run Dead or Alive Millenium in Makaron emulator because it doesn't run full speed in Demul for me.
The modern PC games run at 1280x720 with most quality settings in the middle.
(SSFIVAE, SFxTekken, Mortal Kombat Komplete, Injustice)
Keep in mind that you'll need DirectX11 for the newest versions of Demul and Some of the PC games, so that rules out using Windows XP.