Rob,
What you need is a DVI distribution "amp". And then probably also a Gefen "DVI-Detective". The D-A does, in essence, what any video D-A does, but it's complicated by the EDID data that's exchanged between the displays and the computer.
The Gefen part sits in the cable between the computer and the D-A, after you first "program" it by letting it "see" the EDID data from one of the displays. After that, it merrily impersonates that display by repeating the EDID data --- even if the display is disconnected.
I needed to use this with an XP machine and an ATI X850-based board, because the board needs to see the display's EDID data on boot in order to believe that there's any display connected.
In the end, I've decided to use 1280x720 via the VGA connector to my Samsung DLP, and DVI to my Sony 1292, so I don't need the 1x4 Startech D-A that I bought ... so I'll be selling it, if you're interested, PM me.
Paul