Technically, this is possible. As long as all VGA cards are AGP or PCI, they can coexist. Pile up as many as you please.
This includes chipset-integrated VGA. Note that you can have multiple PCI VGAs, but you can have only one AGP VGA.
This means if you have a chipset integrated AGP VGA and plug an AGP card, the chipset integrated one will disable.
The major pitfall is that the software layers of all cards must be capable of handling the multi-VGA situation -
operating system, VGA BIOSes, and card drivers.
Recently I've seen quite a few NVidia chip based PCI cards that wouldn't even let the system boot when another
VGA is present.
System BIOS might let you choose whether you want the AGP or the 1st PCI VGA card to become the primary
display. Pick your choice before adding the 2nd card.
But alexruiz, why not use a pure TV tuner card?
regards, Peter