I have a flat screen tv and monitor combi i want to add
Yes, it should be possible. I need to ask if you connected your PC through the DVI or RGB input from the back of the computer to the TV. There are 2 main connections for computer monitors. One looks like a plug with 15 pins in 3 rows of 5 (RGB) and the other has 3 rows of 6 (in 2 sections) or 8 (one large section) and and extra larger "blade", possibly with 4 more pins around the blade (DVI).
In either case, you'll need a seperate audio cable to have the audio come through the TV itself. This is a male-male cable with both ends looking like the same ends as for headphones. This should plug in to the back of your TV near the same place as your cable for the video (DVI/RGB). It should be labled "PC Audio" or "PC In" or something similar to that. It should plug in behind the computer tower in either the "Speaker Out" or "Line Out" jack. "Line Out" will usually be set at one volume (regarless of what the computer itself is set at) so you'll be able to change the volume from the TV only.
When turning on the TV with the computer after watching another channel or for the first time, set the volume at 0 or mute the TV, this will prevent blowing out the TV's speakers or your ears.
By the way, I should mention that you should NEVER use a plasma TV for computer use. Only LCD's are designed for computers and video games. I don't know what type of TV you have but plasma's will "burn-in"(show ghost images) of any images that are high contrast and stationary. The same goes for watching any TV channel with a "ticker" on the screen (a black bar at the top or bottom that is in the same spot, usually showing stock market stats, etc.)
After setting up the TV and audio through the TV, you can set up the TV and computer to have 2 seperate monitors if you have a second monitor hooked up to your computer. If you have 2 monitors hooked up, you can have the same image on both, or have 2 completely different things on each monitor. This is done in the "Control Panel" under the START menu of the computer, then go to "Display Settings" on XP or earlier or look under "Appearance and Personalization" where you'll find "Adjust Screen Resolution". Here you can select how you want your monitors to be set up, either "Extend My Desktop" for more space and 2 seperate monitors, or "Clone Desktop" for the same images on both monitors.
If you are having display problems with your TV (screen flickering, desktop looks fuzzy, desktop gets "cut off" at the edges, etc.) this is where you can adjust settings to fix the problem. Try to set the resolution to the highest setting and then the refresh rate at 60hz or higher. Don't worry, if something happens and you can't see your computer on the monitor for any reason while changing these settings, DON'T CLICK ANYTHING OR HIT ANY KEYS and the monitor will automatically reset to the previous setting after about 15 seconds, if you like the settings, click "YES" in the box that asks you if you want to save those settings.
That being said, I hope you have the best of luck getting the most out of your TV and computer with my help and don't forget to rate! If you have any other questions, add it as a comment and I will do my best to help you out. Thank you!