Depends on the inputs available on the current monitors and the new one.
I currently have 3 monitors(27", 26", 19") using DisplayPort, HDMI and DVI as those are the outputs from my graphics card. If the 26" monitors have alternative ports, it'd probably be easier than finding a card with 3 DVI outputs. Newer monitors tend to have HDMI and DVI. Some Dell units have HMDI, DisplayPort, DVI, VGA, Composite and Component (my 27" has all these - pretty useful for testing old hardware).