OK.. I happen to be doing this currently as my TV burnt up last week..
I have 2 monitors and a high end graphics card.
Now the PC will need a TV Tuner card, I happen to be using a Hauppage 1800 HVR in a PCI x1 slot on the main board.
I do recommend XP Media Center 2005 for best performance, however the TV Tuner does come with WinTV 6 and WinTV 2000 applications (the difference is display resolution support)
Now the TV signal I have is Cable coming in through the Cable Converter box.. setting your TV Tuner to channel 3 Analog signal and your TV will display just fine.. if you have Basic or Expanded basic cable, then you can connect the TV Tuner directly to the cable.. the Tuner is capable of recieving up to 150 channels Analog.. with a converter box, then all you need is 1 channel on the turner (Channel 3) and you can control the channels vis the converter remote.
Most TV Tuners come with their own remote which will control the TV Tuner.. but it is mostly designed to operate Windows Media Center.. the remote also interfaces with the Cable Converter box so all you would need is the Tuner remote to switch channels.
Now, my Graphics card is a NVidia Geforce 8800 GTX OC2 with 768 MB gDDR3 memory.. however most vid cards with 256 memory can run the TV tuner.. if you want to game and play TV at the same time, then I would highly recommend a Vid card using 512 MB vid memory (not shared)
The graphics card will either need to have 2 Vid out ports or an interface (like Radeon has) to allow for multiple monitor connect. Most current NVidia's come with 2 dual DVI connects.. Dual DVI is for High Definition play back from the tuner.. if you run a standard VGA cable.. you probably will either need to purchase DVI cables if your monitors support Digital or even High Definition interface, or you will need DVI to VGA adapters to run an analog signal.
Now after hooking up both monitors to the Vid card, your system will have to locate the new device.. I highly recommend installing the Monitor drivers (if drivers are availble for the montior) and then go into your Graphics card properties.
You will then need to go to Configure Monirots section of the Graphics card utility ..
You should have 3 choices.. 1) Single Display Mode.. this is for your primary monitor... 2) Clone mode.. your display is duplicated on both Monitors.. then Dual Monitor Independant Mode, which allows the second monitor to display programs separately from the main monitor.
the Option 3 is what you want for running TV and playing games simultaneously... Your background from your main monitor will be duplicated on both monitors, however you can launch the TV program and drag it to the second monitor, make full screen, then Alt-Tab to change focus, move your mouse pointer back to the main monitor, and then you can launch your game..
The main problem you will have is Sound.. the game and TV tuner use separate processes .. however they share the same speakers..
If you have Surround Sound ports on your PC and 5.1 Surround speakers, then you can actually use 2 of your speakers on the Black port and use your HD Audio Configuration software and remap the Black plug to play just the TV audio, and the Green and Orange connections to speakers for your game sound, thus keeping them separate.
Like I stated.. Windows Media Center is the best way to go to use your TV Tuner.. believe it or not, MCE uses less resources and memory from your computer system to watch TV, not to mention give you a much clearer picture and smooth play back AND it has built in TIVO capabilities built in plus MCE also converts TV to standard DVD playback for normal DVD players.
regular TV Tuners work as TIVO as well, however they record only for PC playback.. no DVD encoding included.
Currently I have a HD WS Flatscreen monitor and an analog monitor using a Dual DVI adapter..
My wife has her TV, and I have my PC for games.. Kind of wierd currently since I am use to surround at my PC and I am now using L, R, Center and Sub for games and my wife has the RL and RR speakers running for the TV Tuner.. I miss my surround.. but it works for us currently..
Hope that this information helps.. if you have any questions.. please post back and I will detail the info more if you need it.