like ws said if it's PCI-E (pci express) then you can get the PCI-E version of arcadeVGA.
if it's a dell, hp, etc and older the usually left the AGP slot off the board..
meaning you'll have 1. onboard, or 2. pci slots (pci is not the same as pci-e)
in which case you'll need a regular "old" pci video card.. you can probably find some older dx7/8 cards, but they're pretty rare since almost all cards was AGP a few years ago, no days almost all of them are pci-express
if you get a card with s-video out it wont do you any good on a arcade monitor.. but you could go with a tv, the image wont be as good specificly because of the way video is transmitted over s-video compared to separate RGB on a arcade monitor.
the good news is a lot of cards can be made to work with a arcade monitor using a hacked vga cable and a little piece of software called soft 15khz.. it basicly does what the arcade vga will do for you but with a lot more flexibility and cheap price.. although it's not a plug and play solution as arcade vga
hope i hav'nt confused you.