guess it really depends on what slots u have on your motherboard. i know ppl running 2 vid cards but if you don't have the slots on your board your kinda screwed. i know my buddy was running an agp and a pci in his crappy comp for dual monitors. just depends on what you have for slots. but i'd suggest just getting a tuner, i have one of the msi vox's that plug into the usb and i like it, works very well.
as i said above, i have an msi vox. which is a tuner that plugs into your usb 2.0 slot. i've had it for about 6 months and used it a ton. the lil thing works great and you can prolly pick one up for about 70 bucks. on top of that you can use it on multiple computers and don't have to open them up. its pretty slick.