Well I've found a pci video card that is extremely cheap and with powerstrip's help it can display arcade frequencies no problem.
The matrox mystique 64bit pci card.
They cost around 1$ plus shipping on ebay and someone is always selling them.
While you might need a fast video card for your primary display, your secondary display can be a pos card. Punch-out and arm-wrestling are the only dual monitor games that come to mind and they are very puny games graphically. (Except xmen 6p, which isn't practical due to control limitations and a few wierd psychio games.) Also I'm not sure if this is still true, but back in the day windows really only used hardware acceleration for the primary display (unless the card is a dual head).
I can't say enough about the mystique. It's a real piece of crap for anything else, but if you want to run arcade frequencies with as little powerstrip tweaking as possible, you can't beat it for the price.