Working and gaming...

Hi. A friend asked me to build him a multi-purpose machine. He needs to run Solidworks on it - requiring a workstation graphics card (probably a cheap Quadro330) - but he also wants to be able to game on it. How do I go about this? Can you put workstation and gaming graphics cards in the one machine without any problems? If so I assume you need a motherboard with 2 PCI-x16 slots - but those boards are often made for SLI or xfire, and this system will have 2 different cards - does that matter? Will/can I need/use 2 seperate DVI cables from each card into the same monitor? How will the computer know which card to use? Sorry, so many questions, but workstations are a mystery to me, let alone combinations...