Quad screen solution

[powerbird101]

i have a dual screen solution with 2 24inch widescreen moniters (viewsonic VP2330wb) side by side on a ergatron dislpay mount ds100 dual. i would like to go to 2 more on top with the quad moniter systembut one of my friends said i would run into a video problemwhere only the 2 moniters on each card can process video on only those moniters and not transfer it to others. I would like to know what i should do once i get these other 2 moniters as i am going to rebuild my computer anyways. Btw is 2 on top and 2 on the bottom a good solution for multiple widescreen moniters?