How u go about it depends largely on the gfx card u have and the drivers that run it.
My dvr laptop is an Inspiron 5150 with an nVidia goFX5200 card.
Using my nVidia drivers I open up the driver software and I see 2 desktop icons, one representing the laptop and the other the TV screen(whatever extra screen you plan on using must be hooked up, and the computer aware of it or else you will not find any options to extend or clone your desktop, at least thats how it is using my drivers).
From there I can launch a wizard that walks me through how I want it setup.
I've never tried extending video to the tv screen while doing something else on the lappy, but I do have the option to do it. I can also drag windows between each screen icon if I want different apps to be viewed seperately on their own screens.
I'm sorry because this probably doesn't help you , so all I can say is fire up your driver software and get into the Help section and try to figure out how to go about doing what u want using your cards software.
I hooked up a couple of tuners to the laptop and then installed the dvr software from snapstream, called BeyondTV. If u go to their website www.snapstream.com
you can download a fully functional copy so you can try it out for 21 days.
Basically its like TIVO without the monthly fees. Pause, rewind, Live TV. Search for shows by name, type, genre etc.
Season pass recording to record all new episodes of a show (very handy for LOST, 24, I record an entire season and then just watch them back to back
, so much more tolerable than agonizing with cliffhanger week after cliffhanger week).
Schedule shows over web or web enabled phone. Stream live tv or recorded shows over web (I use this at work when I'm bored but sparingly because I would probably get fired if caught).
Very nifty stuff, check it out. There are other free apps too like Myth TV but they are hard to configure, but once you do you're set so also good to check em out too especially if you're handy with tinkering and configuring stuff like this.