If it were XP, it'd be cheap and simple to put together.
The thing that makes me nervous with video cards for Vista is that it's hard to "mix 'n match" using different video cards.
So, the good thing is you only want video on 1 monitor. You want inexpensive and you have 2 slots of each type.
My answer would be to use 2 inexpensive pci-e cards side by side. The ones I use usually have 1 analog & 1 DVI port (cheaper). But for Vista, they *should* be exactly the same cards or at least use the *same* driver.
Do you need 2 dvi ports per card?