My customer's Dell Vostro 220 had an nVidia graphics card - the product ID is CN-0N4079-69861, not sure of the exact nVidia model no. - with a DMS-59 connector, hooked up to two monitors with a Molex splitter cable - single DMS-59 at the card end, DVI at each of the monitor ends. This enabled him to run Windows in extended display mode - the desktop extended over the two screens.
This computer's motherboard gave out, and rather than replace the board, the customer bought an HP Pavilion PC with an nVidia GT 530 graphics card. This card has a standard DVI out; I bought a DVI to DVI splitter (StarTech.com DVISPL1DD - 1 ft DVI-D to 2x DVI-D Digital Video Splitter Cable - DVI at the card end and at each monitor end). The PC (running Windows 7 64-bit) shows the same screen on both monitors; extended mode is not available. Windows sees only a single monitor, which it calls a Generic non-PnP monitor. I have updated the graphics card to the latest driver, which is recognised by Win7, and attempted to put the display into extended mode from the nVidia control panel, but Windows still sees only a single generic non-pnp monitor.
To get around this, I uninstalled the graphics card and substituted the one from the old machine. I cannot get a valid driver for it anywhere - nVidia / Geforce websites either don't recognise it or state no Win64 driver available; an extensive Google search doesn't throw up anything useful. Tried using legacy (XP/Vista) drivers - no difference. The result is that Win7 sees that card as a standard VGA display.
I don't think it's the new card - according to the documentation, it should support 2 monitors. Clearly it's not the monitors themselves, as they delivered the right result in the old system. So either it's something to do with Win7's inability to recognise the monitors correctly (monitor drivers?), or it's the splitter cable. I don't think it's anything to with the card - though I could of course be mistaken.