hehe..
Dual Videocards work fine on a single cpu..I mean jezz look at the rig that has dual monitors in my sig...
And thats with WInXP Pro...
Besides the CPU doesnt have actualy render anything for the second card because games will run on which card you have set in as your primary Video card in XP, Which you just simply right click on the monitor that teh card is hooked up under Display properties/ Settings and there are Options such as "Primary", Which will either have a check by it and be greyed out, or you can select it, the other option is "Attached"..this basicly turns that monitor on or off, Most of the time if its off all you do is click it and Windows will ask you to "Attach" it....
Now back to the main problesm so I dont ramble off into confusion.... The reason you are getting a Error saying teh device could not start is because You need to boot off that PCI card and not the AGP... DOnt worry once in Windows XP you can set the AGP card as primary. Sometimes windows is nice enough to remember that the AGP card list as Radeon, Geforce or whatever was the original Primary VGA device and after it shows the WinXP boot screen on the PCI one it will automaticaly pop up on the AGP card and continue load as normal, and install the drivers for the second Video card, if it has them, If its a newer card it will ask you for the drivers and install them... Then it will say you need to reboot in order to use the newly installed device...
Reboot and your pc will boot off the PCI card once again...
When you get into windows you may have to arrange the monitors to how you actualy have them setup on your desk, All you do is Drag the monitor around in the Display properties and Hit apply....
I hope I havent just confused you..
I think I should explain why you need to boot off the PCI card
...This is a motherboard issue most of the time, Something with resources and Windows, But all you have to do is go into your BIOS and set your board to boot off the PCI card...
So whats going to happen from now on once you get everything setup... Your motherboard will boot off the PCI card and then Windows will use the AGP card...
Ill warn you, soem games like castle Wolfinstine wont work with dual monitors and try to use the pci card. or agp over an extended desktop...But when it does this it prevents you from oveing the mouse at all in the game and to fix this you have to exit the game and "Detach" the second monitor/ PCI card so that windows turns it off and relaod the game, it will now only see one registerd Videocard and load off it....This is what the demo of RTCW has done to me for the past few weeks...
I only have xperience with dual monitors involving 2 video cards, I have yet to mess with a video card that will run dual monitors at the same time...But I plan on this...soon...
Hmmm I may write an article one weekend on dual monitors for overclockers.com..Cause I think we need it...